CA1067255A - Sintered shape - Google Patents
Sintered shapeInfo
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- CA1067255A CA1067255A CA320775A CA320775A CA1067255A CA 1067255 A CA1067255 A CA 1067255A CA 320775 A CA320775 A CA 320775A CA 320775 A CA320775 A CA 320775A CA 1067255 A CA1067255 A CA 1067255A
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Abstract
SINTERED SHAPE
ABSTRACT OF THE DISCLOSURE
A highly compact sintered shape having a glassy appearance consists essentially of ferrous-based randomly irregular particles bonded together by molecular diffusion between and at contact points of the particles in the shape.
The shape contains a protective metal, such as, copper, which served to protect the metal particles from oxidation during formation.
ABSTRACT OF THE DISCLOSURE
A highly compact sintered shape having a glassy appearance consists essentially of ferrous-based randomly irregular particles bonded together by molecular diffusion between and at contact points of the particles in the shape.
The shape contains a protective metal, such as, copper, which served to protect the metal particles from oxidation during formation.
Description
The present invention is directed to a sintered shape. This application is a division of copending Canadian application Serial No. 253,158 filed May 21, 1976.
In accordance with the present invention, there is provided the as-sintered shape consisting essentially of ferrous-based particles having a protective metal content thereof no less than 0.05%, the protective metal having a hardness less than that of the particles, a metal temperature below but substantially about the liquidus of the particles and being relatively easy to abrade, the particles being random-ly irregular in configuration and non-spherical, the particles being bonded together by molecular diffusion between and at contact points of the particles in the shape, the shape having no apparent porosity and an outer surface appearing as a melted glassy surface.
The parent application Serial No. 253,158, out of which this application is divided, is concerned with a method of producing an as-sintered shape from scrap metal turnings by refrigerating the turnings to below the transition tempera-ture, impacting them with a fracturing force, and then im-pacting them with an abrading force using protective metal laden elements. The protective metal particles are compacted and the compact sintered. The procedure may be used to form the product of this invention.
The invention is described further, by way of illus-tration, with reference to the accompanying drawings, in which:
Figure 1 is a schematic flow diagram of the pro-cedure of the parent application whereby the product of the invention may be formed;
Figure 2 is a photograph of two sintered shapes, one in accordance with this invention and the other comprising ~.
conventionally-produced from atomized ferrous-based powder;
and F~igure 3 is a photograph of the fracture surface along one end of each of the specimens illustrated in Figure
In accordance with the present invention, there is provided the as-sintered shape consisting essentially of ferrous-based particles having a protective metal content thereof no less than 0.05%, the protective metal having a hardness less than that of the particles, a metal temperature below but substantially about the liquidus of the particles and being relatively easy to abrade, the particles being random-ly irregular in configuration and non-spherical, the particles being bonded together by molecular diffusion between and at contact points of the particles in the shape, the shape having no apparent porosity and an outer surface appearing as a melted glassy surface.
The parent application Serial No. 253,158, out of which this application is divided, is concerned with a method of producing an as-sintered shape from scrap metal turnings by refrigerating the turnings to below the transition tempera-ture, impacting them with a fracturing force, and then im-pacting them with an abrading force using protective metal laden elements. The protective metal particles are compacted and the compact sintered. The procedure may be used to form the product of this invention.
The invention is described further, by way of illus-tration, with reference to the accompanying drawings, in which:
Figure 1 is a schematic flow diagram of the pro-cedure of the parent application whereby the product of the invention may be formed;
Figure 2 is a photograph of two sintered shapes, one in accordance with this invention and the other comprising ~.
conventionally-produced from atomized ferrous-based powder;
and F~igure 3 is a photograph of the fracture surface along one end of each of the specimens illustrated in Figure
2.
A preferred mode of forming the product of this in-vention in accordance with the process of the parent applica~
tion is illustrated in Figure 1. Thus:
(1) Scrap metal and particularly machine turnings 10 are selected as the starting material. "Machine turnings"
is defined herein to mean segments of ribbons of low alloy steel. They typically are shavings cut from alloy bar. But machine turnings, preferably ferrous based, include alloying ingredients such as manganese, silicon, chromium, nickel and molybdenum. The turnings should be selected to have a surface-to-volume ratio of at least 60:1, which is charac-teristic of machine turnings. The scrap pieces ~7;11 have a size characterized by a width 0.1-1.0 inch, thickness of 0.005-.03 inches, and a length of 1-100 inches. Machine turnings are usually not suitable formelting in an electric furnace because they prevent efficient melt down due to such surface-to-volume ratio.
This process can be performed with other types or larger pieces of scrap metal, although capital investment costs may increase due to the difficulty of impacting scrap metal sized in particle pieces beyond .03" thick. The scrap pieces should be selected to be generally compatible in chemistry when in the final product; this is achieved optimally when the scrap is selected from a common machining operation where the same metal stock was utilized in forming the turnings.
106~Z55 (2) The selected scrap pieces 10 are then put into a suitable charging passage 11 leading to a ball milling machine 12 or equivalent impacting device. Within the passage, means 13 for freezing such metal pieces is introduced, such as liquid nitrogen; it is sprayed directly onto the metal pieces.
Mere contact of the liquid nitrogen with the scrap pieces will freeze them instantly. The application of the liquid nitrogen should be applied uniformly throughout its path to the point of impaction. The ball milling elements 14 are motivated pre-ferably by rotation of the housing 17, to contact and impactthe frozen pieces 15 of scrap metal causing them to fracture and be comminuted. Such impaction is carried out to apply sufficient fracturing force (defined to mean less than 1 ft.-lb.) and for sufficient period of time and rate to reduce said scrap pieces to a powder form. The powder 16 will typically have both a coarse and a fine powder proportion.
Both proportions will be comprised of particles which are flake or layered in configuration; each particle will be highly irregular in shape and dimension, none being spherical in shape. A typical screen analysis for copper coated powder would be as follows (for a 100 gram sample):
Mesh No MillingAfter 72 Hrs.
(in grams) (in grams) 60.0 31.5 100 19.5 11.0 200 6.5 18.0 325 4.5 22.5 -325 4.0 9.5
A preferred mode of forming the product of this in-vention in accordance with the process of the parent applica~
tion is illustrated in Figure 1. Thus:
(1) Scrap metal and particularly machine turnings 10 are selected as the starting material. "Machine turnings"
is defined herein to mean segments of ribbons of low alloy steel. They typically are shavings cut from alloy bar. But machine turnings, preferably ferrous based, include alloying ingredients such as manganese, silicon, chromium, nickel and molybdenum. The turnings should be selected to have a surface-to-volume ratio of at least 60:1, which is charac-teristic of machine turnings. The scrap pieces ~7;11 have a size characterized by a width 0.1-1.0 inch, thickness of 0.005-.03 inches, and a length of 1-100 inches. Machine turnings are usually not suitable formelting in an electric furnace because they prevent efficient melt down due to such surface-to-volume ratio.
This process can be performed with other types or larger pieces of scrap metal, although capital investment costs may increase due to the difficulty of impacting scrap metal sized in particle pieces beyond .03" thick. The scrap pieces should be selected to be generally compatible in chemistry when in the final product; this is achieved optimally when the scrap is selected from a common machining operation where the same metal stock was utilized in forming the turnings.
106~Z55 (2) The selected scrap pieces 10 are then put into a suitable charging passage 11 leading to a ball milling machine 12 or equivalent impacting device. Within the passage, means 13 for freezing such metal pieces is introduced, such as liquid nitrogen; it is sprayed directly onto the metal pieces.
Mere contact of the liquid nitrogen with the scrap pieces will freeze them instantly. The application of the liquid nitrogen should be applied uniformly throughout its path to the point of impaction. The ball milling elements 14 are motivated pre-ferably by rotation of the housing 17, to contact and impactthe frozen pieces 15 of scrap metal causing them to fracture and be comminuted. Such impaction is carried out to apply sufficient fracturing force (defined to mean less than 1 ft.-lb.) and for sufficient period of time and rate to reduce said scrap pieces to a powder form. The powder 16 will typically have both a coarse and a fine powder proportion.
Both proportions will be comprised of particles which are flake or layered in configuration; each particle will be highly irregular in shape and dimension, none being spherical in shape. A typical screen analysis for copper coated powder would be as follows (for a 100 gram sample):
Mesh No MillingAfter 72 Hrs.
(in grams) (in grams) 60.0 31.5 100 19.5 11.0 200 6.5 18.0 325 4.5 22.5 -325 4.0 9.5
(3) The commlnuted cryogenic powder 16 is then subjected to another impacting step, but this time at ambient temperature conditions. The powder is placed preferably in another ball milling machine, the machine having copper laden elements 19 preferably in the form of solid copper balls of about .5 inch in diameter. In trials performed herein, the interior chamber was a 3" x 6" cylinder, powder charge was 10 in. 3, and the milling time was a~out 48 hours. Milling time and rate depend on mill volume, mill diameter size of copper balls, and the speed of rotation. The function of this second impacting step is to transfer, by impact, a por-tion of the copper ingredient carried-by the hall milling elements 19 so as to form a copper shell about substantially each particle of the powder 16. The finer powder will obtain a copper coating by true abrasion of scratching with the surface of the ball milling elements 19. Ball milling - elements 19 should have a diameter at least 50 times the lar-gest dimension of any of the particle shapes of the cryogenic powder 16. Secondly, the ball milling operation must gener-ate defect sites in substantially all powder particles above 124 microns; the ball milling operation herein should be carried out so that substantially each coarse particle has at least one defect site therein. This can be accomplished by rotating the housing 20 to impart a predetermined abrading force from the balls 19.
When this step is completed, the particles will be in a condition where they will all substantially have a con-tinuous copper envelope (coating or shell) and be stressed sufficiently so as to have a high degree of cold work. The term l'defect site" is defined herein to mean a defect in local atomic arrangement. The term "copper shell" is defined herein to mean a substantially continuous thin envelope intimately formed on the surface of the particle. Although the shell should preferably be an impervious continuous envelope about each particle, it is not critical that ,it be absolutely im-pervious. It has been shown, by the test examples performed in connection with reducing this invention to practice, that cold working of the particles is predominantly influential in increasing diffusion kinetics of this invention, the copper coating or shell operating to predominantly form an anti-oxidation barrier.
' (4) A predetermined quantity of powder condition from step (3) is compacted by a conventional press 20 to a predetermined density, preferably about 6.6 g./cc. This is brought about by the application of forces in the range of 30-35 tsi. The presence of the copper envelope about the powder particles improves compressibility. With prior un-coated powders, a density of about 6.4 g./cc. is typically obtained using a compressive force of 85,000 psi; with the powder herein, densities of about 6.6 g./cc. are now obtained at the same force level.
The shape 21 into which such powder is compacted is designed to have an outer configuration larger than that desired for the final part. A significant and highly im-proved shrinkage takes place as a result of the next step (5); the shrinkage can be a predetermined known factor and allowance can be made in the compacted shape 21 of this step.
Shrinkage will be in the controlled limits of 15-15.
(5) The compacted shape 21 is subjected to a sintering treatment within a furnace 22 wherein it is heated to a temperature preferably in the range of 2000-3100F, for ferrous based cryogenic powder. The temperature to which the compact is heated should be at least the plastic region for the metal constituting the powder. A controlled or protec-1~67ZSS
tive atmosphere is maintained in the furnace, preferably con-sisting of inert or reducing gases.
At the sintering temperatures, atomic diffusion takes place between particles of the powder particularly at solid contact points therebetween; certain atoms of one par-ticle are supplied to fill the defect sites or absence of certain atoms in the crystal structure of the contacting particle, said defect sites being present as a result of cold working in step (3). Diffusion is accelerated to such an extent, that an increase of more than 100 times is obtained.
It is theorized that at least 60~ of the improvement in physical properties of the resulting sintered shape is due to the controlled cold working of the powder. The increased diffusion is responsible for the increase in shrinkage.
The copper envelope on the particles serves to essen-tially prevent oxidation of certain elements or ingredients within the powder particles, particularly manganese and silicon.
With typical ball milling parameters, (such as physical size of mill speed change and ball size) sufficient to the job, it can be expected that substantially each particle of the cryo-genic powder will possess an impervious copper shell. However, a totally impervious shell is not absolutely essential to obtaining an improvement of some of the properties herein.
As a basis for comparison, several as-sintered test samples were prepared. The procedure for preparing the test samples was varied to investigate aspects such as the effect of cold working, the influence of a copper coating without cold working, the manner in which the copper coating is applied, and the influence of particle size. All of the test 30 samples were prepared according to the following fabrication and thermal treatment except as noted. A cryogenically produced 1~)67Z55 powder quantity was admixed with 1~ zinc stearate (useful as die wall lubricant) and 0.7-0.8% graphite. The admixture was compacted at a pressure of 25 tons/sq.in. into standard M.P.I.F. transverse rupture strength bars. The bars were pre-heated at 1450F for 20 minutes to burn off the lubricants, the heating was carried out in an endothermic type atmosphere at a 45F dew point. Sintering was carried out at a higher temperature in the same endothermic atmosphere for an-addi-tional 20 minutes.
The first three samples are considered represen-tative of the prior art as a reference base since no separate cold working or copper coating was employed.
Sample No. Sintering Transverse Rupture Hardness As-Sintered Temp. (F) Strength (psi) (RB) Density 1 2050 16,000 62 6.5 ~- 2075 20,000 68 6.6 3 2100 22,000 73 6.6 To investigate the effect of cold working, the powder ball milled was in a mill employing steel balls; the ball milling time was varied for each of the three samples in the following sequence: 20 hours, 44 hours and 96 hours.
Sample No. Sintering Transverse Rupture Hardness As-Sintered Temp.(F) Strength (psi) (RB) Density
When this step is completed, the particles will be in a condition where they will all substantially have a con-tinuous copper envelope (coating or shell) and be stressed sufficiently so as to have a high degree of cold work. The term l'defect site" is defined herein to mean a defect in local atomic arrangement. The term "copper shell" is defined herein to mean a substantially continuous thin envelope intimately formed on the surface of the particle. Although the shell should preferably be an impervious continuous envelope about each particle, it is not critical that ,it be absolutely im-pervious. It has been shown, by the test examples performed in connection with reducing this invention to practice, that cold working of the particles is predominantly influential in increasing diffusion kinetics of this invention, the copper coating or shell operating to predominantly form an anti-oxidation barrier.
' (4) A predetermined quantity of powder condition from step (3) is compacted by a conventional press 20 to a predetermined density, preferably about 6.6 g./cc. This is brought about by the application of forces in the range of 30-35 tsi. The presence of the copper envelope about the powder particles improves compressibility. With prior un-coated powders, a density of about 6.4 g./cc. is typically obtained using a compressive force of 85,000 psi; with the powder herein, densities of about 6.6 g./cc. are now obtained at the same force level.
The shape 21 into which such powder is compacted is designed to have an outer configuration larger than that desired for the final part. A significant and highly im-proved shrinkage takes place as a result of the next step (5); the shrinkage can be a predetermined known factor and allowance can be made in the compacted shape 21 of this step.
Shrinkage will be in the controlled limits of 15-15.
(5) The compacted shape 21 is subjected to a sintering treatment within a furnace 22 wherein it is heated to a temperature preferably in the range of 2000-3100F, for ferrous based cryogenic powder. The temperature to which the compact is heated should be at least the plastic region for the metal constituting the powder. A controlled or protec-1~67ZSS
tive atmosphere is maintained in the furnace, preferably con-sisting of inert or reducing gases.
At the sintering temperatures, atomic diffusion takes place between particles of the powder particularly at solid contact points therebetween; certain atoms of one par-ticle are supplied to fill the defect sites or absence of certain atoms in the crystal structure of the contacting particle, said defect sites being present as a result of cold working in step (3). Diffusion is accelerated to such an extent, that an increase of more than 100 times is obtained.
It is theorized that at least 60~ of the improvement in physical properties of the resulting sintered shape is due to the controlled cold working of the powder. The increased diffusion is responsible for the increase in shrinkage.
The copper envelope on the particles serves to essen-tially prevent oxidation of certain elements or ingredients within the powder particles, particularly manganese and silicon.
With typical ball milling parameters, (such as physical size of mill speed change and ball size) sufficient to the job, it can be expected that substantially each particle of the cryo-genic powder will possess an impervious copper shell. However, a totally impervious shell is not absolutely essential to obtaining an improvement of some of the properties herein.
As a basis for comparison, several as-sintered test samples were prepared. The procedure for preparing the test samples was varied to investigate aspects such as the effect of cold working, the influence of a copper coating without cold working, the manner in which the copper coating is applied, and the influence of particle size. All of the test 30 samples were prepared according to the following fabrication and thermal treatment except as noted. A cryogenically produced 1~)67Z55 powder quantity was admixed with 1~ zinc stearate (useful as die wall lubricant) and 0.7-0.8% graphite. The admixture was compacted at a pressure of 25 tons/sq.in. into standard M.P.I.F. transverse rupture strength bars. The bars were pre-heated at 1450F for 20 minutes to burn off the lubricants, the heating was carried out in an endothermic type atmosphere at a 45F dew point. Sintering was carried out at a higher temperature in the same endothermic atmosphere for an-addi-tional 20 minutes.
The first three samples are considered represen-tative of the prior art as a reference base since no separate cold working or copper coating was employed.
Sample No. Sintering Transverse Rupture Hardness As-Sintered Temp. (F) Strength (psi) (RB) Density 1 2050 16,000 62 6.5 ~- 2075 20,000 68 6.6 3 2100 22,000 73 6.6 To investigate the effect of cold working, the powder ball milled was in a mill employing steel balls; the ball milling time was varied for each of the three samples in the following sequence: 20 hours, 44 hours and 96 hours.
Sample No. Sintering Transverse Rupture Hardness As-Sintered Temp.(F) Strength (psi) (RB) Density
4 2100 28,000 - 6.6 Z100 46,000 - 6.6 6 2100 59,000 - 6.3 To further separate or analyze the effect of fine particle sizes, the starting material was not milled but rather it was screened so as to pass fine particles through a 100 mesh screen. The screened fine particles were then sub-jected to the treatment outlined above. The results showed:
Sample No. Sintering Transverse Rupture Hardness As-Sintered Temp.(F) Strength (psi) (RB) Density 7 2100 -25,000 20-25 5.8 An investigation of the influence of copper coating, by itself, without cold working from ball milling elements, was pursued. A copper coating was applied chemically to the particles of the cryogenic powder; for the following first three samples, the coating was applied electrolytically using a copper sulphate (CuSO4) salt in the electroplating bath and the next two samples were prepared u~ilizing a copper nitrate (CuN03) salt.
Sample No. Sintering Transverse Rupture ~ness As-Sintered Temp.(F) Strength (psi) (~) Density 8 2100 3,000 - 5.5(no special handling) 9 2100 5,000 - 6.0(the pcwder was pretreated in HCl before plating) 2100 15,000 - 6.5(an alcohol rinse was applied after plating) 11 2100 18,000 - 6.5(no special handling) 12 2100 12,000 - 6.4(an alcohol rinse was applied after plating) An investigation was made as to whether fine parti-cles, simply copper coated, would provide an improvement. The copper coating was again applied electrolytically utilizing a copper nitrate (cuNQ3) salt, the powder particles were restricted to ~100 mesh.
Sample No. Sintering Transverse Rupture Hardness As-Sintered Temp.(F) Strength (psi) (~) Density 13 2100 72,000 - 6.2 Finally, the combined effect of (a) cold working through a ball milling operation and (b) the application of g :~Q672S5 a copper enve]ope or coating on each of the particles at the same time the ball milling is carried out, was investigated.
It is important to point out that the copper coating was applied mechanically by an abrading action between copper balls and the cryogenic powder within the milling machine.
Fine particles below 120 mesh probably obtained a copper coating merely by abrading of the soft copper thereonto, while the coarser particle achieved a copper envelope much more by abrading action along with receiving cold work. The ball milling was carried out for a period of 96 hours. The results were as follows:
Sample No. Sintering Transverse Rupture Hardness As-Sintered-Temp.(F) Strength (psi) (~) Density 14 210~ 90,000 84 6.7 By ball milling for extended periods of time or at an increased stress rate, a transverse rupture strength of at least 95,000 can be obtained. Accordingly, it is conGluded that not only is the transverse rupture strength improved by the combination effect herein but such improvement is beyond that obtainable by utilizing conventional atom~zed powder under the same processing conditions but without cold work or copper coating. Typically, atomized powder will obtain at best a transverse rupture strength of 85,000 psi with a density of around 6.7g-/cc. when processed under the most favor~ble conditions known to the prior art. Accordingly, with the decrease in cost by use of scrap materials reduced to a powder cryogenically along with the improvement in physical characteristics herein, important advantages have been obtained.
Other conclusions which can be drawn from the above data include: (a) the general effect of cold working by ball milling increases the sinterability of the cryogenically pro-~Q67Z55 duced powder, (b) decreasing the average particle size of thepowder has little effect by itself on the final physical pro-perties, (c) copper coating, by itself, appears only to im-prove sinterability of fine powders, and (d) the combination of cold working and copper coating by use of copper balls, increases the sintered strength 4-5 fold.
Turning now to Figures 2 and 3, there is illustra-ted comparative examples of an as-sintered shape. The sample in the left hand portion of Figures 2 and 3 represents a shape produced in accordance with this invention utilizing cryo-genically produced powder and processed with a second ball milling operation where cold working and copper coating is obtained. The sample in the right hand portion in each of the photographs represents an as-sintered shape obtained by conventional powder metallurgy techniques utilizing ordinary atomized iron powder. Such ordinary atomized powder typically consists of primarily 99.1% iron, the remainder may consist of:
carbon .01-.045%; silicon .005-.015%; sulphur .004-.016;
phosphorus .007-.027; Mn .04-.26%; residual oxides - weight loss in ~2 is .2%-.6%. The atomized powder was merely sub-jected to a compacting step achieving a green density of about 6.4, and was subjected to heating at a sintering temperature of 2050F.
In Figure 2, the right-hand sample of this invention has a particularly evident smooth outer surface as opposed to the relative rough heterogeneously shaded outer surface for the sample on the left. Figure 3 shows the end face where fracture took place as a result of destructive testing. The sample on the left has a typical fracture, rough and highly porous surface. The sample on the right has a fibrous appear-ance. The as-sintered shape of this invention is particularly 1067ZSCi !
ccmprlsed of ferrous particles which are randomly irregular in configuration, none of which are spherical; the particles are bound together by molecular diffusion at contact points therebetween, ~aid shape having no apparent porosity and has a fractured surface as a result of destructive testing which appears as glassy. It is further characterized by a weight to volume ratio of 6.6-6.7, a typical transverse rupture strength of 95,000 psi with the compact at a density of 6.6-6.7 g./cc. (resulting from compression forces of 25-30 tsi). The hardness of such as-sintered shape is at least 84 RB.
A new powder compact has been achieved as a result of practicing a portion of the disclosure herein. Such powder compact uniquely consists essentially of uniformly and homo-geneously mixed ferrous based particles having a proportion of fine particles in the size range of ~200-325 and a coarse particle proportion in the size range of +60-140, the fine particles be~ng present in the ratio of 1:1 to the coarse particles, the fine and coarse particles each have a copper envelope about substantially each of the coarse particles thereof, and substantially each of the coarse particles have at least one defect site therein, said compact having a den-sity of at least 6.6 g./cc. and a volume shrinkage of about 10% upon being heated to 2050F.
.
Sample No. Sintering Transverse Rupture Hardness As-Sintered Temp.(F) Strength (psi) (RB) Density 7 2100 -25,000 20-25 5.8 An investigation of the influence of copper coating, by itself, without cold working from ball milling elements, was pursued. A copper coating was applied chemically to the particles of the cryogenic powder; for the following first three samples, the coating was applied electrolytically using a copper sulphate (CuSO4) salt in the electroplating bath and the next two samples were prepared u~ilizing a copper nitrate (CuN03) salt.
Sample No. Sintering Transverse Rupture ~ness As-Sintered Temp.(F) Strength (psi) (~) Density 8 2100 3,000 - 5.5(no special handling) 9 2100 5,000 - 6.0(the pcwder was pretreated in HCl before plating) 2100 15,000 - 6.5(an alcohol rinse was applied after plating) 11 2100 18,000 - 6.5(no special handling) 12 2100 12,000 - 6.4(an alcohol rinse was applied after plating) An investigation was made as to whether fine parti-cles, simply copper coated, would provide an improvement. The copper coating was again applied electrolytically utilizing a copper nitrate (cuNQ3) salt, the powder particles were restricted to ~100 mesh.
Sample No. Sintering Transverse Rupture Hardness As-Sintered Temp.(F) Strength (psi) (~) Density 13 2100 72,000 - 6.2 Finally, the combined effect of (a) cold working through a ball milling operation and (b) the application of g :~Q672S5 a copper enve]ope or coating on each of the particles at the same time the ball milling is carried out, was investigated.
It is important to point out that the copper coating was applied mechanically by an abrading action between copper balls and the cryogenic powder within the milling machine.
Fine particles below 120 mesh probably obtained a copper coating merely by abrading of the soft copper thereonto, while the coarser particle achieved a copper envelope much more by abrading action along with receiving cold work. The ball milling was carried out for a period of 96 hours. The results were as follows:
Sample No. Sintering Transverse Rupture Hardness As-Sintered-Temp.(F) Strength (psi) (~) Density 14 210~ 90,000 84 6.7 By ball milling for extended periods of time or at an increased stress rate, a transverse rupture strength of at least 95,000 can be obtained. Accordingly, it is conGluded that not only is the transverse rupture strength improved by the combination effect herein but such improvement is beyond that obtainable by utilizing conventional atom~zed powder under the same processing conditions but without cold work or copper coating. Typically, atomized powder will obtain at best a transverse rupture strength of 85,000 psi with a density of around 6.7g-/cc. when processed under the most favor~ble conditions known to the prior art. Accordingly, with the decrease in cost by use of scrap materials reduced to a powder cryogenically along with the improvement in physical characteristics herein, important advantages have been obtained.
Other conclusions which can be drawn from the above data include: (a) the general effect of cold working by ball milling increases the sinterability of the cryogenically pro-~Q67Z55 duced powder, (b) decreasing the average particle size of thepowder has little effect by itself on the final physical pro-perties, (c) copper coating, by itself, appears only to im-prove sinterability of fine powders, and (d) the combination of cold working and copper coating by use of copper balls, increases the sintered strength 4-5 fold.
Turning now to Figures 2 and 3, there is illustra-ted comparative examples of an as-sintered shape. The sample in the left hand portion of Figures 2 and 3 represents a shape produced in accordance with this invention utilizing cryo-genically produced powder and processed with a second ball milling operation where cold working and copper coating is obtained. The sample in the right hand portion in each of the photographs represents an as-sintered shape obtained by conventional powder metallurgy techniques utilizing ordinary atomized iron powder. Such ordinary atomized powder typically consists of primarily 99.1% iron, the remainder may consist of:
carbon .01-.045%; silicon .005-.015%; sulphur .004-.016;
phosphorus .007-.027; Mn .04-.26%; residual oxides - weight loss in ~2 is .2%-.6%. The atomized powder was merely sub-jected to a compacting step achieving a green density of about 6.4, and was subjected to heating at a sintering temperature of 2050F.
In Figure 2, the right-hand sample of this invention has a particularly evident smooth outer surface as opposed to the relative rough heterogeneously shaded outer surface for the sample on the left. Figure 3 shows the end face where fracture took place as a result of destructive testing. The sample on the left has a typical fracture, rough and highly porous surface. The sample on the right has a fibrous appear-ance. The as-sintered shape of this invention is particularly 1067ZSCi !
ccmprlsed of ferrous particles which are randomly irregular in configuration, none of which are spherical; the particles are bound together by molecular diffusion at contact points therebetween, ~aid shape having no apparent porosity and has a fractured surface as a result of destructive testing which appears as glassy. It is further characterized by a weight to volume ratio of 6.6-6.7, a typical transverse rupture strength of 95,000 psi with the compact at a density of 6.6-6.7 g./cc. (resulting from compression forces of 25-30 tsi). The hardness of such as-sintered shape is at least 84 RB.
A new powder compact has been achieved as a result of practicing a portion of the disclosure herein. Such powder compact uniquely consists essentially of uniformly and homo-geneously mixed ferrous based particles having a proportion of fine particles in the size range of ~200-325 and a coarse particle proportion in the size range of +60-140, the fine particles be~ng present in the ratio of 1:1 to the coarse particles, the fine and coarse particles each have a copper envelope about substantially each of the coarse particles thereof, and substantially each of the coarse particles have at least one defect site therein, said compact having a den-sity of at least 6.6 g./cc. and a volume shrinkage of about 10% upon being heated to 2050F.
.
Claims (3)
1. The as-sintered shape consisting essentially of ferrous based particles having a protective metal content thereof no less than 0.05%, said protective metal having a hardness less than that of the particles, a metal tempera-ture below but substantially about the liquidus of said particles and being relatively easy to abrade, said particles being randomly irregular in configuration and non-spherical, said particles being bonded together by molecular diffusion between and at contact points of said particles in said shape, said shape having no apparent porosity and an outer surface appearing as a melted glassy surface.
2. The product of claim 1 wherein said protective metal is copper.
3. The product of claim 1 or 2 having a weight-to-volume ratio of 6.6 to 6.7 and a hardness of at least 84 RB.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA320775A CA1067255A (en) | 1975-06-06 | 1979-02-02 | Sintered shape |
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US58456475A | 1975-06-06 | 1975-06-06 | |
| CA253,158A CA1061513A (en) | 1975-06-06 | 1976-05-21 | Method for improving the sinterability of cryogenically-produced iron powder (a) |
| CA320775A CA1067255A (en) | 1975-06-06 | 1979-02-02 | Sintered shape |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1067255A true CA1067255A (en) | 1979-12-04 |
Family
ID=27164490
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA320775A Expired CA1067255A (en) | 1975-06-06 | 1979-02-02 | Sintered shape |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1067255A (en) |
-
1979
- 1979-02-02 CA CA320775A patent/CA1067255A/en not_active Expired
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