AUSTRALIA Patents Act 1990 COMPLETE SPECIFICATION Standard Patent Applicant (s): Sandvik Intellectual Property AB Invention Title: METAL MATRIX PICK The following statement is a full description of this invention, including the best method for performing it known to me/us: - 2 METAL MATRIX PICK Field of the Invention 5 The present invention relates to mining picks used for mining and excavation purposes, and particularly but not exclusively to a mining pick that has a relatively low propensity to ignite a flammable substance adjacent the pick when used. 10 Background of the Invention Various different forms of equipment and machinery can be employed for mining and excavation operations, such is as long wall miners. The present invention is principally concerned with underground coal mining and one of the major safety difficulties in that type of mining relates to fires or explosions within the mine. These can occur due to the generation during mining of methane gas and 20 coal dust (commonly known as mine dust), which can be trapped within the mine and is readily ignitable. Disadvantageously, the equipment used in coal mining can generate heat and/or incendive sparks that may initiate a fire or explosion, especially from frictional contact with 25 coarse grained quartz containing lithologies. Therefore, it is important that all appropriate steps be taken to minimize or eliminate the risk of ignition. Equipment used to mine or excavate in hard earth can 30 include rotary cutters, in which a rotating drum that carries a plurality of projecting cutting bits or picks, is brought into engagement with an earth face. The picks bite into the earth face as they rotate with the drum, to impact against and to dislodge or fragment earth from the 35 face. This highly aggressive engagement between the picks and the earth face can generate heat and/or sparks. 23555131 (GHMatters) 30'07/10 - 3 Prior art picks employed for the above purpose generally have a hard cemented tungsten carbide tip that is fixed, usually by brazing, to a steel shank. Sparks can be produced between the tungsten carbide tip and the earth 5 face and also between the steel shank and the earth face, although there typically is greater likelihood of spark production between the shank and the earth face. Summary of Invention 10 Some embodiments of the present invention may be used in underground coal mining. It will therefore be convenient to describe the invention in relation to that use although it will be readily appreciated that the is invention could be employed for any mining or excavation operation to which its function is suitable. According to a first aspect of the invention there is provided a mining pick, the pick comprising: 20 a body; at least part of the body being formed of a metal matrix composite comprising particles dispersed in a metal; a cutting element mounted to the body; 25 a shank extending from the body; the at least part of the body formed of the metal matrix composite being configured to provide a barrier during an excavation operation, the metal matrix composite has less propensity to cause ignition of a flammable 30 substance adjacent the body during excavation than cemented carbide. In an embodiment, the at least part of the body formed of the metal matrix composite is configured to 35 provide a barrier disposed adjacent to a distal end of the body, the barrier protecting at least a portion of the mining pick disposed between the barrier and a proximal 27556721 (GHMatters) P84673.AU 23/08/11 -4 end of the shank. The barrier may protect the shank. In an embodiment, the at least part of the body formed of the metal matrix composite is configured to 5 provide a barrier after the cutting element fails. In an embodiment, the at least part of the body formed of the metal matrix composite forms an exterior surface of the body adjacent the cutting element. The 10 exterior surface may encircle the cutting element. In an embodiment, the metal matrix composite has a lower propensity to cause ignition of a flammable substance adjacent the body during excavation than a 15 material of the shank. The material of the shank may comprise a steel, or any other suitable material In an embodiment, the metal matrix composite has less propensity to cause ignition of a flammable substance 20 adjacent the body during excavation than a material of the cutting element. In an embodiment, the particles have a hardness 25 greater than 1000 Hardness Vickers and a modulus greater than around 200 Gigapascals. The particles may have a thermal conductivity lower than around 100 W/m/C). In an embodiment, the metal has a hardness and a 30 modulus less than the particles. The metal may have a thermal conductivity greater than around 100 W/m/C). In an embodiment, the particles constitute between 27556721 (GHMatters) P84673 AU 23108/11 - 4A 20% and 90% by volume of the metal matrix composite. In an embodiment, the metal constitutes between 10% and 80% by volume of the metal matrix composite. 27556721 (GHMatters) P84673.AU 23/08/11 - 5 In an embodiment, the particles in the metal matrix composite are tungsten carbide. The tungsten carbide particles may constitute around 60% by volume of the metal 5 matrix composite. In an embodiment, the particles comprise steel. In an embodiment, the metal comprises copper, silver 10 and zinc. The metal may comprise 65% to 75% by volume copper, 5% to 15% by volume silver and 15% to 25% by volume zinc. In an embodiment, the metal is copper. 15 In an embodiment, the metal matrix composite comprises at least one of tungsten carbide, vanadium, chromium, silicon, boron, a carbide forming element, a metal carbide, copper, zinc, manganese, tin, iron, and 20 silver. In an embodiment, the metal matrix composite constitutes the body. The shank may have an end embedded in the metal matrix composite. Alternatively, the metal 25 matrix composite constitutes both the body and the shank. The shank may be integral with the body. In an embodiment, the cutting element is mechanically attached to the metal matrix composite. At least one 30 transverse dimension of at least some of the cutting element may increase in a direction inward of the body. The at least some of the cutting element may be embedded in the metal matrix composite. 35 In an embodiment, the cutting element is metallurgically attached to the metal matrix composite. The cutting element may be attached to the metal matrix 23555131 (GHMatters) 3007f10 -6 composite by a metallurgical high temperature braze. In an embodiment, the cutting element is attached to the metal matrix composite by a sintered bond. 5 In an embodiment, a portion of the cutting element is embedded in the metal matrix composite. In an embodiment, the cutting element comprises 10 thermally stable silicon carbide diamond composite (SCDC). The cutting element may have a surface bonded to a product of a reaction of a metal with the SCDC. The product may be bonded to the metal matrix composite. 15 In an embodiment, the body comprises a plurality of monoliths. The monoliths may comprise at least one of diamond, cermet, ceramic, and cemented carbide. The plurality of monoliths may be embedded in a plurality of carbide containing pellets which are imbedded in the metal 20 matrix compound. The plurality of monoliths may be disposed adjacent the exterior surface of the body near the cutting element. In an embodiment, the body comprises at least two 25 portions, each portion having a respective metal matrix composite, one of the metal matrix composites having a composition that is different to that of the other metal matrix composite. One of the portions may be disposed at a distal end of the body. Another of the at least two 30 portions may be disposed at a proximal end of the body. One of the portions may be disposed in a pocket formed in another of the at least two portions. The pocket may have the cutting element disposed therein. 35 In an embodiment, the body comprises a ring of material encircling the cutting element, the ring having an equal or lesser hardness than that of the cutting 27556721 (GHMatters) P84673.AU 23/08/11 - 7 element and greater than that of the metal matrix composite. In an embodiment, the body has a portion disposed 5 at a distal end comprising a metal matrix composite and another portion disposed at a proximal end comprising a steel. The portion comprising a steel may be integral with the shank. 10 In an embodiment, the mining pick is configured as a point attack pick. In an embodiment, the mining pick is configured as a radial attack pick. 15 In an embodiment, the mining pick is configured to couple to a mining apparatus by a pair of cooperating elements that engage when the mining pick and the mining apparatus are so coupled, each of the pair of elements 20 being disposed on one of the shank and apparatus respectively. According to a second aspect of the invention there is provided a method of making a mining pick, the 25 method comprising the steps of: disposing a powder used in the manufacture of a metal matrix composite in a mould of complementary shape to at least a portion of a body of a mining pick, the portion being configured to provide a barrier during an 30 Excavation operation; heating the powder to a temperature for a period of time to form the metal matrix composite that has the shape of the at least the portion of the body, the metal matrix composite has less propensity to cause ignition of 35 a flammable substance adjacent the body during the excavation operation than cemented carbide. 27556721 (GHMatters) P84673.AU 23/08/11 - 7A Brief description of the Figures Features and advantages of the present invention will become apparent from the following description of s embodiments thereof, by way of example only, with 27556721 (GHMatters) P84673 AU 23/08/11 - 8 reference to the accompanying drawings, in which: Figure 1 shows a side elevation view of an embodiment of a mining pick in accordance to an aspect of the invention; 5 Figure 2 shows a cross section through a cutting element bonded to a metal matrix composite body via a product of a reaction, in accordance with an embodiment of an aspect of the invention; Figure 3 shows a cross section through an example of 10 a cutting element that is mechanically attached to a respective body in accordance with an embodiment of an aspect of the invention; Figure 4 shows a cross section through a cutting element and respective body wherein the body comprises a is plurality of very hard monoliths in accordance with an embodiment of an aspect of the invention; Figure 5 shows a cross section through a cutting element and a respective body having a continuous ring of very hard material, such as cemented carbide, encircling 20 the cutting element in accordance with an embodiment of an aspect of the invention; Figure 6 shows a side elevation view of an embodiment of a mining pick having a body comprising first and second portions, each portion having a respective metal matrix 25 composite in accordance with an embodiment of an aspect of the invention; Figure 7 shows a side elevation view of an another embodiment of a mining pick having a body comprising first and second portions, each portion having a respective 30 metal matrix composite in accordance with an embodiment of an aspect of the invention; Figure 8 shows a side elevation view of another embodiment of a mining pick have a body comprising steel and metal matrix composite in accordance with an aspect of 35 the invention; and Figure 9 is a graph showing probability curves of two embodiments of a mining pick having respective metal 23555131 (GHMatters) 30/07110 - 9 matrix body portions causing ignition in comparison to a prior art mining pick, over the respective lives of the picks. 5 Detailed Description of embodiments of the invention Figure 1 shows a side elevation view of an embodiment of a mining pick generally indicated by the numeral 10. This embodiment is symmetric around a central axis. The 10 pick has a body 12. In this embodiment the body 12 is formed of a metal matrix composite comprising particles dispersed in a metal. In some other embodiments, however, only a part of the body is formed of the metal matrix composite. 15 The pick 10 of this embodiment has at a distal end thereof 22 a cutting element 14 configured to cut, fracture, wear, plough or otherwise remove material from a formation in use. Examples of formations include 20 geological formations such as a body of coal, and man made structures. The cutting element 14 is in the form of an insert or tip having a ballistic shape. It will be appreciated that any suitable cutting element may be used. In this embodiment, a portion of the insert is disposed in 25 a pocket 22 formed at a distal end 15 of the pick body 12. The pocket is indicated by dashing. The insert 14 is attached to the side and/or bottom walls of the pocket. The pick has at a proximal end 13 a shank 16 30 extending from a proximal end 26 of the body 12. The shank is one of by a pair of cooperating elements that engage when the pick and the rotary drum of the mining machine are coupled. The other of the pair of elements is disposed on the rotary drum. The shank includes a recess 18. A 35 clip engages the shoulders of the recess to retain the pick at the drum. A portion of the shank is embedded in the metal matrix composite body and this portion is 23555131 (GHMatters) 30/07/10 - 10 indicated by dashing. In this embodiment the shank comprises an air hardening steel and is joined to the metal matrix composite by a high temperature braze, although the shank may be formed of any suitable material. s In another embodiment, the metal matrix composite constitutes both the body and the shank, and the shank is integral with the body (as would be represented by figure 1 if the dashed triangle with a round apex, in that figure, was deleted)- A pick embodiment having a body and 10 a shank made from a contiguous metal matrix composite may have less steps during its manufacture than that of a pick embodiment having a body and shank separately formed and subsequently joined. 15 The mining pick 10 is configured as a point attack mining pick, however it will be appreciated that alternative embodiments may be configured as a radial attack mining pick. 20 In the embodiment of Figure 1, the cutting element 14 is formed of a cemented carbide comprising tungsten carbide particles dispersed in metallic cobalt (alternatively metallic nickel or metallic iron, for example), and the body 12 is formed from a metal matrix 25 composite comprising around 60% by volume tungsten carbide particles dispersed in a metal. The metal of this embodiment comprises around 70% by volume copper, 10% by volume silver and 20% by volume zinc. Five other examples of compositions of a metal for use in forming a matrix 30 composite are listed in Table 1, although it will be appreciated that there are many other compositions not listed in the table. 2355131 (GHMatters) 30/07/10 - 11 Table 1. Some alternative metal compositions by volume %. Cu Zn Mn Ni Ag Sn Pb 1 60-95 40-5 (<10) (<10) 2 60-95 40-5 (<10) (<10) 3 60-95 30-5 10-0 (<10) (<10) 4 60-95 20-5 10-0 10-0 (<10) (<10) 5 60-95 35-5 (<10) (<10) s The applicant has unexpectedly found that the body 12, comprising the metal matrix composite, did not produce a spark on contact with a workshop grinder wheel rotating at high speed. The wheel comprises resin bonded ceramic. The wheel simulates an environment that is more severe 10 than that typically experienced by the pick 10 during excavation. Contact between the cemented carbide cutting tip 14 and the wheel, however, produced sparks. Contact between the steel shank 16 with the wheel produced a proliferation of sparks. The applicant has also found is that a metal matrix composite body comprising steel particles dispersed in cooper also has a low propensity to spark. This was very much unexpected especially in light of the fact that steel generally has a propensity to spark. 20 The reason for the particularly low propensity of the metal matrix composite body to produce a spark is not known by the applicant definitively, however the applicant is of the opinion that the metal within the metal matrix 25 composite may act as a contiguous path for the flow of heat away from the point of contact and so prevent the build up of heat and sparking. 23555131 (GHMatters) 30/07/10 - 12 In use, the tip 14 engages the formation. Fragments cut from the formation may contact the metal matrix composite exterior surface 20 disposed at a distal end 15 of the body adjacent the cutting element 14. The exterior 5 surface 20 encircles the cutting element 14. The metal matrix composite surface 20 acts as a barrier against the fragments, protecting at least a portion of the mining pick disposed between the barrier 20 and a proximal end 17 of the shank 16. Even if some of the surface 20 is worn 10 away a barrier is still provided by the exposed metal matrix composite. If the cutting element penetrates the formation deeply and the body is dragged across the formation the surface 20 will provide a barrier against the formation. 15 As described, the metal matrix composite barrier has a relatively lower propensity to spark and contact of the fragments with the exterior surface 20 is unlikely to produce a spark. Typically the barrier 20 greatly reduces 20 the chance of a fragment striking the shank 16, or any other component of the pick that may present an ignition risk, for example. The distal end 26 of the body is wider than the shank 25 16, and thus the barrier provides a region protected from fragments that encompass more than the shank. In the embodiment of Figure 1 the protected region is around 1.3 times the width of the shank. Other embodiments have a protected area width of 3 times the width of the shank. 30 By way of contrast, prior art mining picks, particularly those having a body formed of steel, may heat up and/or spark during excavation. Hot and/or sparking picks have been known to ignite methane and/or coal dust 35 in mines. Thus, use of the pick embodiment of figure 1 instead of a prior art pick may greatly reduce the incidence of friction induced ignition during excavation 2366513_1 (GHMatters) 30/07/10 - 13 which is very dangerous in a mine, for example. It is not uncommon during excavation for a cutting element to fail. For example, the element 14 may shear 5 off adjacent the surface 20 or become dislodged from the pocket 22. In this case, the surface 20, which now may extend to include the surface of the pocket 22, provides a wear resistant barrier with a low propensity to ignite a flammable material. Even if the body is subsequently 10 dragged across the formation it is unlikely that this would cause ignition. In prior art devices, the fragments may wear the body or shank so that the pick becomes unusable before the tip 15 wears out. The barrier, being much harder than steel, for example, may protect the shank and/or other parts of the pick 10 from fragments which may otherwise cause the pick to reach the end of its working life prematurely. In contrast, the use of a super or ultra hard insert within a 20 metal matrix body provides extended tool life and productivity. It will be appreciated that in an embodiment, the shank and body may both be formed of a metal matrix 25 composite. Some properties of metal matrix composites that may form at least part of a pick having a low propensity to cause ignition will now be described. The particles may 30 have hardness greater than 1000 Hardness Vickers and a modulus greater than around 200 Gigapascals. The thermal conductivity of the particles may be less than 100 W/m/C. The metal may have a hardness and a modulus less than the particles. In some but not all embodiments, the thermal 35 conductivity of the metal may be greater than 100 W/m/C, although metals having a higher thermal conductivity such as cooper (around 400 W/m/C) may be preferable in some 23555131 (GHMatters) 30710 - 14 circumstances, especially if heat needs to leave the point of contact more rapidly because of aggressive excavation. The metal matrix composite may comprise at least one of tungsten carbide, vanadium, chromium, silicon, boron, a 5 carbide forming element, a metal carbide, copper, zinc, manganese, tin, iron, and silver. The particles may constitute between :20% and 90% by volume of the metal matrix composite, and the metal constitutes between 10% and 80% by volume of the metal matrix composite. 10 Various techniques may be employed to mount a cutting element such as 14 to a body such as 20. In the embodiment of figure 1, the cemented carbide cutting element 14 is attached to the metal matrix composite 12 by 15 a metallurgical high temperature braze. In making the pick 10, a powder containing the particles to be included in the metal matrix composite is disposed in a mould of complementary shape to at least a portion of a body, and the cutting part is disposed in the mould and in contact 20 with the powder. A metal, such as copper, typically in the form of pellets, is disposed over the powder. Subsequently heating the mould in a furnace for a period of time causes the metal to melt and infiltrate and bind the powder to form the metal matrix composite which 25 permanently adopts the shape of the body on cooling, and simultaneously forms the braze. The temperature of the furnace is typically in the range of 900 to 1200 degrees centigrade, and the mould is typically in the furnace for between 5 and 90 minutes. In the case of the manufacture 30 of a metal matrix composite made using silver-zinc-copper metal together with a tungsten carbide powder, the furnace temperature is around 1050 centigrade and the mould is typically in the furnace for 45 minutes. 35 Alternatively, a cutting element may be attached to the metal matrix composite by a sintered bond. In making picks of this embodiment, the powder and cutting element 27556721 (GHMatters) P84673.AU 23/08/11 - 15 are disposed in a mould, and mechanical pressure is applied to the powder while being heated in a furnace and a low pressure atmosphere. The powder may comprise at least one of cobalt, iron and carbides. A metal may be s optionally disposed in the mould during heating to form a metal binder. In an embodiment, the cutting element comprises polycrystalline diamond compact (PDC) which degrades in 10 air at temperatures above around 750 degrees centigrade. In this case, during the making of the pick at least one pocket forming element may be disposed in a mould and the powder disposed around the at least one element. The at least one element may be removed after the powder is is caused to adopt the shape of at least a portion of the body providing a pocket in the body into which the PDC cutting element may be disposed. The PDC cutting element may then be brazed using conventional silver soldering techniques, for example. The pocket forming element may 20 comprise, for example, graphite or sand. An embodiment of a mining pick has a cutting element comprising thermally stable silicon carbide diamond composite (SCDC). The cutting element has a surface 25 coated by a product of a reaction of a metal with the SCDC, and the product is bonded to both the metal matrix composite and the cutting element. In this case, during the making of the pick, elements that form carbides and/or take carbon into solution may be disposed in the mould. 30 The SCDC cutting element is prior coated with a metal such as titanium, silicon, and tungsten using, for example, using a chemical or physical vapour deposition process. During heating the chemical bond between the SCDC, metal coating, and metal matrix composite is formed. In some 35 circumstances a plating (another coating) may be applied to the metal coating, such as a nickel, iron or copper plating. The additional plating may prevent 27556721 (GHMatters) P84673.AU 23/08/11 - 16 oxidation during processing. Figure 2 shows a cross section through an example of a SCDC cutting element 30 bonded to a metal matrix composite body 32 via a product of the reaction, which in this case is a metal carbide 34. 5 Other methods of chemical retention of the SCDC insert include the addition of carbide and/or solution forming elements of diamond/carbon. Such elements include but are not restricted to chromium, titanium and tungsten. During the making of the pick, these elements may be dispersed in 10 the powder, or more desirably locally around the SCDC insert. During liquid metal infiltration transport of these elements bond to the diamond through the formation of carbides and/or by taking the diamond surface into solution. Other approaches include the use of a high 15 manganese containing binder or the local insertion of active braze metals at or around the SCDC prior to infiltration Figure 3 shows a cross section through an example of 20 a cutting element 40 that is mechanically attached to a respective body 42. At least one transverse dimension of at least some of the portion embedded in the metal matrix composite increases in a direction 44 inward of the body 42. The portion embedded in the metal matrix composite 25 mechanically interferes with a complementarily shaped pocket providing resistance to separation of the cutting element 40 from the body 42. Generally, any tapered, cap, or dove tail geometry may be used. The bottom of the cutting element 40, which is embedded in the metal matrix 30 composite, gently transitions to the side rather than having an abrupt transition marked by a corner, for example. Avoiding corners reduces stress concentration which assists in reducing the probability of fracture of the metal matrix composite during excavation, especially 35 in the case of the end of the cutting element being embedded in a metal matrix composite which may have a relatively low fracture toughness compared with other 27556721 (GHMatters) P84673 AU 23108/11 - 17 materials such as a steel. Figure 4 shows a cross section through an example of a cutting element 50 and respective body 52 wherein the 5 body comprises a plurality of very hard monoliths such as 54. This may improve wear resistance of the body. Each monolith may comprise, for example, diamond 56, a cermet 58, a ceramic 60, and a cemented carbide 62. The plurality of monoliths 54 to 62, in this but not necessarily all 10 embodiments, are embedded in a plurality of carbide containing pellets which are in turn imbedded in the metal matrix composite 52. The plurality of monoliths are disposed adjacent a surface of the body. The monolith may be arranged in a ring around the cutting element. 15 In another embodiment, diamond or other ceramic particles can be dispersed throughout the metal matrix composite or added to the surface locations occupied by monoliths shown in Figure 4. These diamond and/or ceramic 20 particles can be also incorporated within a carbide containing pellet. Figure 5 shows a cross section through an example of a cut-ting element 70 and a respective body 72 having a 25 continuous ring 74 of very hard material, such as cemented carbide, encircling the cutting element. The ring 74 may be bonded to the metal matrix composite 76 by a high temperature braze. The ring 74 would typically have an equal or lesser hardness than that of the cutting element 30 and greater than the metal matrix composite 76. Benefits of the ring include intimate and improved wear resistance compared with a metal matrix composite without additions. The maximum width Dl of the cutting part is greater than an inner circumference D2 of the ring 74. While it may be 35 advantageous in view of wear resistance to form the entire pick from cemented carbide, this is typically prohibitively expensive. The pick embodiment of Figure 5, 23555131 (GHMatters) 30/07110 - 18 however, provides better wear resistance than the pick embodiment of Figure 1 and may still be economical. When a SCDC cutting element is used there may not by a bond between the cutting element and the metal matrix 5 composite. Mechanical retention is thus assisted by the ring 74, which has an inner circumference D2 less than the maximum outer circumference D1 of the cutting element. Figure 6 shows a side elevation view of an embodiment 10 of a mining pick 80 having a body 82 comprising first 84 and second 86 portions, each portion having a respective metal matrix composite. The first portion 84 is adjacent a proximal end of the body and may comprise a material that is softer, cheaper and/or easier to make, than that is of the second portion 86. The second portion 86 is located adjacent a distal end of the body and adjacent to the tip 88 and so is more wear resistant than the first portion 84. This approach may reduce the cost of the pick 80 compared with a pick having the entire body comprising 20 a hard metal matrix composite. Figure 7 shows a side elevation view of an another embodiment of a mining pick 90 having a body 92 comprising first 94 and second 96 portions, each portion having a 2s respective metal matrix composite. The metal matrix 96 is more ductile than 94, to increase toughness and fracture resistance adjacent the cutting element 98 which may reduce the likelihood of cracking and failure of the metal matrix composite adjacent the cutting element. This may 30 be achieved by including iron, steel, copper, tungsten, or molybdenum, for example, in portion 96. Metal matrix composite 94 may be harder than metal matrix composite 96 providing improved wear resistance and protection of metal matrix composite 96. 35 Figure 8 shows a side elevation view of another embodiment of a mining pick 100. In this embodiment, the 23555131 (GHMatterS) 30/07/10 - 19 proximal end 101 of the body has a portion 102 comprising, for example, a steel and another portion 104 at a distal end 106 comprising a metal matrix composite 104. The metal matrix composite portion 104 may be sufficient 5 protection and reduce the propensity of the pick to cause ignition when used. The steel portion 102 and the metal matrix composite portion 104 may be joined by, for example, a pair of cooperating elements such as a thread on each of the portions 102 and 104, shrink fitting, 10 chemical or metallurgical bonding etc. Alternatively, the shank and the steel portion of the body may be formed of the one piece of steel. Some of the relatively expensive metal matrix composite has been substituted in this embodiment for relatively inexpensive steel reducing 15 costs. Also, the configuration of the distal end 106 of the pick may be kept constant across a range of embodiments while the proximal end 108 is adapted to engage machines having various pick coupling configurations. 20 Figure 9 is a graph showing, for two embodiments 120,130 of a mining pick having respective metal matrix body portions, the probability of causing ignition in comparison to a prior art mining pick 110 over their 25 respective lives. One embodiment 120 has a cemented carbide cutting element, and the other 130 has a silicon carbide diamond (SCDC) cutting element. Both embodiments 120, 130 have at least a portion of the body comprising metal matrix composite at a distal end. The probability of 30 ignition when using the embodiments 120,130 is lower than that when using the prior art pick 110. Prior art pick 110 has a body comprising only steel and a cemented carbide cutting element (insert). Region A 35 corresponds to the period of usage wherein the cutting element is not significantly worn. Region B corresponds to the period of usage where the cutting element exhibits 23555131 (GHMatter) 30107/10 - 20 significant wear. The probability of ignition increases as the cemented carbide blunts and creates more fine particles during cutting. Region C corresponds to a period after the cutting element fails. The cutting s element may be lost or broken, for example, or worn down to or near the level of the body and the steel body is exposed. Sparking is very likely and the risk of frictional ignition very high. 10 While in Figure 9 Region B is shown to correspond to periods of identical length in the case of the prior art device 110 and the embodiment 120, in some embodiments the wear resistant metal matrix composite may in fact extend Region B so that it is longer than the corresponding 15 Region B for the prior art device 110. A SCDC cutting element such as that of embodiment 130 stays sharp for a significantly longer period than an equivalent cemented carbide cutting element and shows no 20 significant propensity for sparking. In the case pick embodiment 130, Region A is about 10 to 100 times longer than that for prior art pick 110. The probability of ignition in Region A is low. If and when the SCDC insert is lost (Region C) and the matrix directly contacts the 25 formation the probability of ignition is significantly lower than that of either the prior art pick or the embodiment of the pick having a metal matrix body portion with the cemented carbide cutting element in place. Thus, it may be desirable to use in some circumstances a pick 30 embodiment having a SCDC cutting element and a body with at least a portion comprising a metal matrix composite, in view of the prolonged tool life and productivity and the low probability of ignition. 35 It is to be understood that, if any prior art publication is referred to herein, such reference does not constitute an admission that the publication forms a part 2355131 (GHMatter) 30/07/10 - 21 of the common general knowledge in the art, in Australia or any other country. In the claims which follow and in the preceding 5 description of the invention, except where the context requires otherwise due to express language or necessary implication, the word "comprise" or variations such as "comprises" or "comprising" is used in an inclusive sense, i.e. to specify the presence of the stated features but 10 not to preclude the presence or addition of further features in various embodiments of the invention. It will be understood to persons skilled in the art of the invention that many modifications may be made 15 without departing from the spirit and scope of the invention. For example, the cutting element may comprise a rotary cutter. 23555131 (GHMatters) 30/07/10