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Iron & steel
Literature
Review~~~~~~~~~~~!!!!
Composites with whisker volume. fraction lVr) ranging from0 to 40% were fabricated by a powder metallurgical method. In a low Vr range. the ultimate tensile strength increases proportionally with the increase in Vrandagreessatisfactorilywith the value calculated from Kelly and Tyson's equation. Ina high Vrrange. however,the increasing rate of strength becomes smaller and a decrease in strength is observed in higher strength aluminum alloy matrix composites due to a decrease in ductility. The elastic modulus increases as the Vr increases and is in good agreement with the value calculated from Cox's equation. APPLICATION OF LOW·EXPANSION HIGH·MODULUS ALUMINUM ALLOY PROCESSED BY RAPIJI SOLIDIFICATION H Inoue, et al, Kobe SteelEngineering Reports. Vol. 40, No.1, 1990, 66-68. In Japanese. The application of rapidly solidified lRS) AI-Si alloys to precision machinery parts is discussed. The addition of Si up to 30 wt% reduces specific weight and thermal expansion, and increases modulus of elasticity in accordance with the law of mixtures. Toolabrasion during machining of the RS alloys containing up to 35 wt% Si was almost comparable to that with conventional alloys containing up to 18 wt%. Featuring a high specific modulus, low thermal expansion and good machinability, the RS AI-Si alloy has wide applicability to quick movingparts in various kinds of precision machinery.
Iron & Steel
MECHANICAL PROPERTIES OF RAPIDLY SOLIDIFIED IRON BASED ALLOYS B L Mordike, et al.Tl'cchnische Univ. Clausthal, W Germany). Proceeding '8th German-Yugoslav Meeting on Materials Science and Development: Ceramics and Metals'. P. 385-392. In German. Highcarboncast irons wereproduced by combining PM and rapid solidification techniques. Alloys were produced in powder form by gas or water atomization and then consolidated by extrusion or hot isostatic processing and submitted to a thermomechanicaltreatment. The alloys produced show high tensile strength and acceptable ductility. WEAR RESISTANT SINTERED STEEL WITH lIIGH CARBIDE CONTENT R Klausmann, et al.Ikarlsruhe Univ, W Germany). Proc, '8th Corman-Yugoslav Meeting on Materials Scienceand Development: Ceramicsand Metals'. P. 353·361. In German. Sintered steels with 10 to 30 vol.% of special carbides were developed by mechanical alloying, pressing, and liquid phase sintering. The best results are achieved with systems where the carbide phase is added as fine carbide powder, which does not take part in liquid phase formation, but is provided by addition of P or PtC. Especially in Fe-NbC-P and Fe·t\'bC-P-C systems, very high 374
densification and equal and fine distribution of the carbide phase in the heat treatable matrix are reached.
studied, and sintering rate of Fe-Wand Fc-Ni alloys were further studied quantitatively by measurements of neck growth between their wires.
EFFECT OF CONTINUOUS COOLING ON TIlE MICROSTRUCTURE AND MECHANICAL PROPERTIES OF SINTERED LOWALLOY STEELS
EFFECT OF Cm.WACTING PRESSURE AND SINTERING TDWERATURE ONMECHANICAL PROPERTIES OF SINTERED IRONPOWDER PREPLATED wrrn ELECTROLESS Ni
M Kamada, et al, J. Japan Soc. Powder and Powder Metallurgy, Vol. 36, No.8, 1989, 93·99.
C A Loto (Obaferni Awolowo University, Ile-Ifc, Nigeria). Canadian Metallurgical Quart. Vol. 28, No.3, 1989. 259-263.
In order to improve the mechanical properties of sintered low alloy steels, Fe·1.5%Si-2.0%NilO.5%Mo)·0.1-0.5%C compacts sintered at 1250C for3.6ks were cooled in variousconditions afterthe solution treatment at 960C. The structures of specimens were controlledby changingthe cooling rate. The relation between the structures which transformed during continuous cooling and the mechanical properties was studied. The results are summarized as follows: On the continuous coolingtransformation diagram. the addition of Mo shifted the ferrite and pearlite noses to longer time and enlarged the sections of bainitic and martensitic transformations. It was necessary, under the optimum carbon content and cooling rate, to get the fine mixed structure of polygonal ferrite, bainitic ferrite and upper bainite which resulted in good combination of strength, ductility and toughness. But lower bainite and martensite appeared constantly in the structure of the specimens cooled in uniform cooling rate and decreased the ductility and toughness. The STEP cooling, which was the treatment of changing the coolingrate at 600C,leadto the fine mixedstructure mentioned above containing 10-25 vol% retained austenite. The STEP cooled specimens showed good mechanical properties; for example in 0.3-0.4%C specimen, 750 MPa of tensile strength, 8% of elongation and 120 kJ/m2 of Charpy impact value. POWDER EXTRUDED BEARING STEEL ASalek,et ai, POlI'der Met. Int., Vol.22,No.1, 27-29. Basicdata are given aboutextruded powder bearing steel rods and wires. Powder was produced by nitrogen atomization of remelted machining swarf. The properties of this steel in the as-extruded state are on the same level as annealed wrought bearing steels. Strength properties, fracture toughness and rolling contact fatigue endurance were measured. Durability of ball bearingswith the inner and outer rings of extruded steel were tested. The rolling contact fatigue endurance was 2,5x higher than that of wrought bearing steel. An analysis of fracture piltings and microstructure of extruded powder specimens outlined the required powder properties and extrusion and heat-treatment conditions for optimization and stabilityimprovementofcomplex properties bearing steel bars produced by this method. The results predict a reasonablechance for powder metallurgy, to be used for metal scrap recycling. SINTERING BEHAVIOUR OF Fe·W AND Fe·Ni ALLOYS AT HIGHTEMPERATURE
An investigation of the effect of compacting pressure and sintering temperature on the mechanicaland physical properties of sintered iron powder pre-platedwith elcctrolessnickel wasmade using four different fractions of the powder and a dilute solution of commercialnickel sulphamate at a pH of 4.8 and a temperature of 90C. The results obtained with varied compacting pressures and sintering temperatures for the mechanical and physical properties of the sintered products, suggest that a good homogeneity was obtained. There wasan increasein elongationand a shrinkage in the thickness of the sintered compacts. Sintered strength and density increase with the growth in compacting pressure and in nickel content. A considerable increase in sintered strength and elongation was obtained with the growth in sintering temperature. CHARACTERISTICS OF IIIGH-STRENGTII SINTERED CO~IPONENTS USING LOW ALLOYED STEEL POWDER T Miyashita, et al, Kobe Steel Engineering Reports, Vol. 40. No.1, 1990.7 ·10. In Japanese. For sintered components used mainly in the automobile industry where recent demand calls for high strength, a new partially prealloyed powder and a prealloyedsteelpowder havebeen developed. For mechanical properties, the new powders achieve an impact value of 2-3 kgf.m/cm! and tensile strength of 120-130 kgf/mrn". Through use ofthe 2P2Sprocess,tensile strength of160 kgf/mm? has been attained. DEVELOPMENT OF ODS ALLOYS BY MECHANICAL ALLOYING METIfOD M Fujiwara. T Nishida, Kobe Steel Engineering
Reports, Vol. 40, No.1, 1990. 58-61. In Japanese. The effectsofY20 J content and Ti, Mo additions on the elevated- temperature strength of oxide dispersion strengthened 12Crsteels prepared by the mechanical alloying method is examined. The strength increases with Y20J content and is remarkablyimprovedby addition ofTi to the matrix steel. This is attributed to the formation of fine mixed Y-Ti oxides and their dispersion hardening. Strength is also improved by the addition of Mo. This is attributed to the combined effectsofsolution and dispersion hardening.
S Tanabe, et al, J. Japan Soc. Powder and Powder Metallurgy, Vol. 36, No.8. 81-86. In Japanese.
DEVELOPMENT OF CO~[POSITE IIIGH·ALLOY WORK ROLL TIlROUGH APPLICATION OF IIIP BmmING TECIL,,\OLOGY
In order 10 examine sintering behaviour in a and y phases of iron based mixed powder compacts, the sintering process of Fe and W mixed powders was
YDetani,ct al, Kobe SteelEngineering Reports, Vol. 40, No.1, 1990.34·37. In Japanese. MPR May 1990
~~~~~~~~~~~!!!!!!!f.Literature It was shown that the newly developed roll.
manufactured from high C and high Cr tool steel powder material. gives better results in both wear and thermal shock tests and good mechanical properties at the bonded zone of the roll when compared with those ofa conventionalsolid roll. In order to obtain the specified hardness- and heat-penetration depths. the quenching conditions have been investigated and optimized for the progressive induction hardeningmethod. Basedon these results. a composite high-alloy work roll produced by IIII' honding has been developed for cold strip mills. BEHAVIOUR OF DIMENSIONAL CHANGE IN SINTERING OF FE·BASED POWDERS Z Takata.et al, Kobe SteelEngineering Reports. Vol. 40. No 1. 1990. 11-14. In Japanese.
tetragonal structures. were identified as the principal second phases in these alloys. Strength decreased steadily as temperature increased above 700K. as diffusion-assisted mechanisms. including grain boundary sliding and cavitation. became operative.Althoughall alloyshad similarstrengths at 1100 K. Hf additions significantly improved high-temperature ductility by suppressing cavitation.
Nickel Alloys
Review
data on effectsof microalloying on proccssabllity, microstructure and mechanical properties are not readily available. To develop some data. tantalum powder with various levels of silicon (0-50 ppm) was processed under identical conditions. Sheet samples were then annealed at different temperatures and evaluated via microstructural. chemical and mechanical tests. The recrystallization temperature was found to increase with silicon content.mostprobablyasa resultofthe presence of an intorrnctallic (TajSf) phase. The mechanical propertiesofunrecrystalllzed tantalum are. as expected. significantly different from those of recrystallized tantalum.
NEW CARBIDES IN THE Ni·Ti·Mo-C SYSTEM Y Hashimoto. et al, J. Japan Soc. Powder and POII'der Metallurgy. Vol. 36. No.8. 1989. 22-26. In Japanese.
Titanium
Alloys
A STIJDY OF A SINTERED Ti ALLOY A study of the dimensional change in the compact of Fe-2 \\1% Cu- 0.8 wt%Gr-0.75 \\1% Zn-st was carried out systematically by simulating the operating conditions in a practical sintering furnace. The abnormal expansion which occurs in the a-Fe range after delubricating is caused by gas carburizingand has considerableeffecton sintering behaviour. The dimensional change becomes smallerwith carburizingduring heatingand greater with carburizing during cooling.
The structures of two new Ti-Mo carbide phases observed in the system Ni-Mo-Ti-C at toOOC are described. One is hexagonal and the other is orthorhombic. The system was studied by X-ray diffraction and optical and electron microscopy. Micrographs arc given.
MICROSTRUCTURAL STUDIES OF ULTRAFINE Fe PARTICLES
PARTICLE BONDING, ANNEAUNG RESPONSE AND MECHANICAL PROPERTIES OF DYNA~nCALLY CONSOLIDATED 304 STAINLESS STEEL POWDERS
S Wang. et al, [Inst. of Metal Research. Academica Sinica,Shenyang.China). ActaMet. Sinica, Vol. 25. No.5. 1989. 358- 360. In Chinese. The constitution. structure and surface state of the ultraflne iron particles preparedby gas evaporation technique havebeen investigated by meansofX-ray analysis. high-resolution electron microscopy and electron spectroscopy for chemical analysis. The results showed that the fine particles arc spherical ones of - 20nm in diameter with n-Fe cores and covered by Fe30. fine crystalline layers of -4nm thickness. MICROSTRUCTURE AND TENSILE PROPERTIES OF Fe-40at%AI ALLOYES WITH ADDITIONS OF C. z-, llf AND B D J Gaydosh. et al. (NASA Lewis Research Centre. Cleveland.Ohio. USA). Metallurgical TransA. Vol. 20. No.9. 1989. 1701-1714. The influence of small additions of C. Zr, and Hf, alone or in combination with B. on the microstructure and tensile behaviour of substolchiometric FeAl was investigated. Tensile properties were determined from 300 to 1100K on powder which was consolidated by hot extrusion. All materials possessed some ductility at room temperature. although ternary additions generally reduced ductility compared to the binary alloy. Adding B to the C- and Zr-containing alloys changed the fracture mode from intergranular to transgranular and restored the ductility to approximately 5% elongation. Additions of Zr and !If increasedstrength up to about 900 K. which was related to a combination of grain refinement and precipitation hardening. Fe6Al6Zr and Fe6Al6IIf precipitates. both with identical body-centered
MPR May 1990
Stainless Steel
RNWright. ct al, (E.GandGIdahoInc.•IdahoFalls. USA). Metallurgical Trans A.. Vol. 20A. No. 11. 1989.2249-2458. The nature of interparticle bonding in explosively consolidated. centrifugally atomized (CA). and vacuum gas-atomized (VGA) Type 304 stainless steel powders has been examined. Stress waves with sufficientamplitudeto producefulldensitydo not necessarily produce metallurgical bonds betweenparticles;the localstrain and strain ratearc found to determine the degreeof local heatingand. in tum. the degree of particle fusion. Particle interaction is found to be limited to nearest neighbours. The as- consolidated CA material has approximatelytwicetheultimatetensilestrengthof mill-annealed wrought Type 304 stainless steel. Consolidated CA powder has a higher defect density than VGA powder consolidated under the same conditions; however, the VGA material recrystallizes at a lowertemperaturedue to a lower concentration of carbides. Annealing explosively consolidatedmaterialproducedfromeither powder results in sintering, improved particlebonding.and greater ductility.
Tantalum EfFECT OF Si ON PROPERTIES OF Ta K D Moser. et al, (Cabot Corporation. Boyertown. PA, USA). J Metals (TMS). October1989.50-53. Themicroalloying oftantalumwith silicon hasbeen effectively used on a commercial scale. However,
K Majima, J. Japan Soc. Powder and Powder Metallurgy. Vol. 36.No.8.1989. 41-49. In Japanese. The effectofcutcctoid ~ stabilizingclementson the sinteringcharacteristics ofTi powdercompacts was carried out in order to get the high dense sintercd Ti alloy by the conventional sinlering method through a blended elemental process.The addition of Fe. Ni and Co among eutectoid ~ stabilizing clements showed the excellent effect on the densification of Ti powder compacts. where the sintered density ratio of Ti-4 mass% Co specimen washigherthan 99%.and both of theirratiosofTi-4 mass%Fe and Ti- 4 mass%Ni were higher than 98%. The tensile properties for sintered Ti-4 mass%Co and Ti-4 Fe specimens were remarkably improved by (a + ~)-quenching after ~-solution treatment. and the corrosion resistance of Ti-4 mass%Fespecimen in both of physiological saline solution and IN-Hel solution was confinned to be better than those of Ti-6 AI-4 V specimen or Ti-5 AI-2.5Fe specimenwhich was newly developed as implanted material. In addition. the implantation test maintained in the tibia ofrabbit for 14 months showedthatTi-4Fespecimenhad theexcellentbiocompatability.
MICROSTRUCTUREIPROCESSING RELATIONSHIPS INIIIGII·ENERGY IIIGH-RATE CONSOLIDATED PO\\'DER COl\IPOSITES OF l'.'b·STABIUZED TiJAI + TiAI C Persad, et al, (Texas University. Austin. USA). ProceedingofMaterials Research Society.Vol. 133. 1989.717-722. A new approach to powderprocessing is employed in forming titanium alurninide composites. The processingconsistsof internal heating of a powder blend by a fast electrical discharge of 'lMJ in IS'. Pulse permits rapid heating of an electrically conductingpowdermixturein a cold wall die.This short time at temperature approach offers the opportunity to control phase transformations and the degreeofmicrostructural coarseningnot readily possible with standard powder processing approaches.This paperdescribesthe consolidation results of titanium aluminide- based powder compositematerials. Thefocusofthis study wasthe definition of microstructure/processing relationships for each of the composite constituents. first as monoliths and then in composite forms. Non-equilibrium phases present 375
Review~~~~~~~~~~~!!!!
Composites with whisker volume. fraction lVr) ranging from0 to 40% were fabricated by a powder metallurgical method. In a low Vr range. the ultimate tensile strength increases proportionally with the increase in Vrandagreessatisfactorilywith the value calculated from Kelly and Tyson's equation. Ina high Vrrange. however,the increasing rate of strength becomes smaller and a decrease in strength is observed in higher strength aluminum alloy matrix composites due to a decrease in ductility. The elastic modulus increases as the Vr increases and is in good agreement with the value calculated from Cox's equation. APPLICATION OF LOW·EXPANSION HIGH·MODULUS ALUMINUM ALLOY PROCESSED BY RAPIJI SOLIDIFICATION H Inoue, et al, Kobe SteelEngineering Reports. Vol. 40, No.1, 1990, 66-68. In Japanese. The application of rapidly solidified lRS) AI-Si alloys to precision machinery parts is discussed. The addition of Si up to 30 wt% reduces specific weight and thermal expansion, and increases modulus of elasticity in accordance with the law of mixtures. Toolabrasion during machining of the RS alloys containing up to 35 wt% Si was almost comparable to that with conventional alloys containing up to 18 wt%. Featuring a high specific modulus, low thermal expansion and good machinability, the RS AI-Si alloy has wide applicability to quick movingparts in various kinds of precision machinery.
Iron & Steel
MECHANICAL PROPERTIES OF RAPIDLY SOLIDIFIED IRON BASED ALLOYS B L Mordike, et al.Tl'cchnische Univ. Clausthal, W Germany). Proceeding '8th German-Yugoslav Meeting on Materials Science and Development: Ceramics and Metals'. P. 385-392. In German. Highcarboncast irons wereproduced by combining PM and rapid solidification techniques. Alloys were produced in powder form by gas or water atomization and then consolidated by extrusion or hot isostatic processing and submitted to a thermomechanicaltreatment. The alloys produced show high tensile strength and acceptable ductility. WEAR RESISTANT SINTERED STEEL WITH lIIGH CARBIDE CONTENT R Klausmann, et al.Ikarlsruhe Univ, W Germany). Proc, '8th Corman-Yugoslav Meeting on Materials Scienceand Development: Ceramicsand Metals'. P. 353·361. In German. Sintered steels with 10 to 30 vol.% of special carbides were developed by mechanical alloying, pressing, and liquid phase sintering. The best results are achieved with systems where the carbide phase is added as fine carbide powder, which does not take part in liquid phase formation, but is provided by addition of P or PtC. Especially in Fe-NbC-P and Fe·t\'bC-P-C systems, very high 374
densification and equal and fine distribution of the carbide phase in the heat treatable matrix are reached.
studied, and sintering rate of Fe-Wand Fc-Ni alloys were further studied quantitatively by measurements of neck growth between their wires.
EFFECT OF CONTINUOUS COOLING ON TIlE MICROSTRUCTURE AND MECHANICAL PROPERTIES OF SINTERED LOWALLOY STEELS
EFFECT OF Cm.WACTING PRESSURE AND SINTERING TDWERATURE ONMECHANICAL PROPERTIES OF SINTERED IRONPOWDER PREPLATED wrrn ELECTROLESS Ni
M Kamada, et al, J. Japan Soc. Powder and Powder Metallurgy, Vol. 36, No.8, 1989, 93·99.
C A Loto (Obaferni Awolowo University, Ile-Ifc, Nigeria). Canadian Metallurgical Quart. Vol. 28, No.3, 1989. 259-263.
In order to improve the mechanical properties of sintered low alloy steels, Fe·1.5%Si-2.0%NilO.5%Mo)·0.1-0.5%C compacts sintered at 1250C for3.6ks were cooled in variousconditions afterthe solution treatment at 960C. The structures of specimens were controlledby changingthe cooling rate. The relation between the structures which transformed during continuous cooling and the mechanical properties was studied. The results are summarized as follows: On the continuous coolingtransformation diagram. the addition of Mo shifted the ferrite and pearlite noses to longer time and enlarged the sections of bainitic and martensitic transformations. It was necessary, under the optimum carbon content and cooling rate, to get the fine mixed structure of polygonal ferrite, bainitic ferrite and upper bainite which resulted in good combination of strength, ductility and toughness. But lower bainite and martensite appeared constantly in the structure of the specimens cooled in uniform cooling rate and decreased the ductility and toughness. The STEP cooling, which was the treatment of changing the coolingrate at 600C,leadto the fine mixedstructure mentioned above containing 10-25 vol% retained austenite. The STEP cooled specimens showed good mechanical properties; for example in 0.3-0.4%C specimen, 750 MPa of tensile strength, 8% of elongation and 120 kJ/m2 of Charpy impact value. POWDER EXTRUDED BEARING STEEL ASalek,et ai, POlI'der Met. Int., Vol.22,No.1, 27-29. Basicdata are given aboutextruded powder bearing steel rods and wires. Powder was produced by nitrogen atomization of remelted machining swarf. The properties of this steel in the as-extruded state are on the same level as annealed wrought bearing steels. Strength properties, fracture toughness and rolling contact fatigue endurance were measured. Durability of ball bearingswith the inner and outer rings of extruded steel were tested. The rolling contact fatigue endurance was 2,5x higher than that of wrought bearing steel. An analysis of fracture piltings and microstructure of extruded powder specimens outlined the required powder properties and extrusion and heat-treatment conditions for optimization and stabilityimprovementofcomplex properties bearing steel bars produced by this method. The results predict a reasonablechance for powder metallurgy, to be used for metal scrap recycling. SINTERING BEHAVIOUR OF Fe·W AND Fe·Ni ALLOYS AT HIGHTEMPERATURE
An investigation of the effect of compacting pressure and sintering temperature on the mechanicaland physical properties of sintered iron powder pre-platedwith elcctrolessnickel wasmade using four different fractions of the powder and a dilute solution of commercialnickel sulphamate at a pH of 4.8 and a temperature of 90C. The results obtained with varied compacting pressures and sintering temperatures for the mechanical and physical properties of the sintered products, suggest that a good homogeneity was obtained. There wasan increasein elongationand a shrinkage in the thickness of the sintered compacts. Sintered strength and density increase with the growth in compacting pressure and in nickel content. A considerable increase in sintered strength and elongation was obtained with the growth in sintering temperature. CHARACTERISTICS OF IIIGH-STRENGTII SINTERED CO~IPONENTS USING LOW ALLOYED STEEL POWDER T Miyashita, et al, Kobe Steel Engineering Reports, Vol. 40. No.1, 1990.7 ·10. In Japanese. For sintered components used mainly in the automobile industry where recent demand calls for high strength, a new partially prealloyed powder and a prealloyedsteelpowder havebeen developed. For mechanical properties, the new powders achieve an impact value of 2-3 kgf.m/cm! and tensile strength of 120-130 kgf/mrn". Through use ofthe 2P2Sprocess,tensile strength of160 kgf/mm? has been attained. DEVELOPMENT OF ODS ALLOYS BY MECHANICAL ALLOYING METIfOD M Fujiwara. T Nishida, Kobe Steel Engineering
Reports, Vol. 40, No.1, 1990. 58-61. In Japanese. The effectsofY20 J content and Ti, Mo additions on the elevated- temperature strength of oxide dispersion strengthened 12Crsteels prepared by the mechanical alloying method is examined. The strength increases with Y20J content and is remarkablyimprovedby addition ofTi to the matrix steel. This is attributed to the formation of fine mixed Y-Ti oxides and their dispersion hardening. Strength is also improved by the addition of Mo. This is attributed to the combined effectsofsolution and dispersion hardening.
S Tanabe, et al, J. Japan Soc. Powder and Powder Metallurgy, Vol. 36, No.8. 81-86. In Japanese.
DEVELOPMENT OF CO~[POSITE IIIGH·ALLOY WORK ROLL TIlROUGH APPLICATION OF IIIP BmmING TECIL,,\OLOGY
In order 10 examine sintering behaviour in a and y phases of iron based mixed powder compacts, the sintering process of Fe and W mixed powders was
YDetani,ct al, Kobe SteelEngineering Reports, Vol. 40, No.1, 1990.34·37. In Japanese. MPR May 1990
~~~~~~~~~~~!!!!!!!f.Literature It was shown that the newly developed roll.
manufactured from high C and high Cr tool steel powder material. gives better results in both wear and thermal shock tests and good mechanical properties at the bonded zone of the roll when compared with those ofa conventionalsolid roll. In order to obtain the specified hardness- and heat-penetration depths. the quenching conditions have been investigated and optimized for the progressive induction hardeningmethod. Basedon these results. a composite high-alloy work roll produced by IIII' honding has been developed for cold strip mills. BEHAVIOUR OF DIMENSIONAL CHANGE IN SINTERING OF FE·BASED POWDERS Z Takata.et al, Kobe SteelEngineering Reports. Vol. 40. No 1. 1990. 11-14. In Japanese.
tetragonal structures. were identified as the principal second phases in these alloys. Strength decreased steadily as temperature increased above 700K. as diffusion-assisted mechanisms. including grain boundary sliding and cavitation. became operative.Althoughall alloyshad similarstrengths at 1100 K. Hf additions significantly improved high-temperature ductility by suppressing cavitation.
Nickel Alloys
Review
data on effectsof microalloying on proccssabllity, microstructure and mechanical properties are not readily available. To develop some data. tantalum powder with various levels of silicon (0-50 ppm) was processed under identical conditions. Sheet samples were then annealed at different temperatures and evaluated via microstructural. chemical and mechanical tests. The recrystallization temperature was found to increase with silicon content.mostprobablyasa resultofthe presence of an intorrnctallic (TajSf) phase. The mechanical propertiesofunrecrystalllzed tantalum are. as expected. significantly different from those of recrystallized tantalum.
NEW CARBIDES IN THE Ni·Ti·Mo-C SYSTEM Y Hashimoto. et al, J. Japan Soc. Powder and POII'der Metallurgy. Vol. 36. No.8. 1989. 22-26. In Japanese.
Titanium
Alloys
A STIJDY OF A SINTERED Ti ALLOY A study of the dimensional change in the compact of Fe-2 \\1% Cu- 0.8 wt%Gr-0.75 \\1% Zn-st was carried out systematically by simulating the operating conditions in a practical sintering furnace. The abnormal expansion which occurs in the a-Fe range after delubricating is caused by gas carburizingand has considerableeffecton sintering behaviour. The dimensional change becomes smallerwith carburizingduring heatingand greater with carburizing during cooling.
The structures of two new Ti-Mo carbide phases observed in the system Ni-Mo-Ti-C at toOOC are described. One is hexagonal and the other is orthorhombic. The system was studied by X-ray diffraction and optical and electron microscopy. Micrographs arc given.
MICROSTRUCTURAL STUDIES OF ULTRAFINE Fe PARTICLES
PARTICLE BONDING, ANNEAUNG RESPONSE AND MECHANICAL PROPERTIES OF DYNA~nCALLY CONSOLIDATED 304 STAINLESS STEEL POWDERS
S Wang. et al, [Inst. of Metal Research. Academica Sinica,Shenyang.China). ActaMet. Sinica, Vol. 25. No.5. 1989. 358- 360. In Chinese. The constitution. structure and surface state of the ultraflne iron particles preparedby gas evaporation technique havebeen investigated by meansofX-ray analysis. high-resolution electron microscopy and electron spectroscopy for chemical analysis. The results showed that the fine particles arc spherical ones of - 20nm in diameter with n-Fe cores and covered by Fe30. fine crystalline layers of -4nm thickness. MICROSTRUCTURE AND TENSILE PROPERTIES OF Fe-40at%AI ALLOYES WITH ADDITIONS OF C. z-, llf AND B D J Gaydosh. et al. (NASA Lewis Research Centre. Cleveland.Ohio. USA). Metallurgical TransA. Vol. 20. No.9. 1989. 1701-1714. The influence of small additions of C. Zr, and Hf, alone or in combination with B. on the microstructure and tensile behaviour of substolchiometric FeAl was investigated. Tensile properties were determined from 300 to 1100K on powder which was consolidated by hot extrusion. All materials possessed some ductility at room temperature. although ternary additions generally reduced ductility compared to the binary alloy. Adding B to the C- and Zr-containing alloys changed the fracture mode from intergranular to transgranular and restored the ductility to approximately 5% elongation. Additions of Zr and !If increasedstrength up to about 900 K. which was related to a combination of grain refinement and precipitation hardening. Fe6Al6Zr and Fe6Al6IIf precipitates. both with identical body-centered
MPR May 1990
Stainless Steel
RNWright. ct al, (E.GandGIdahoInc.•IdahoFalls. USA). Metallurgical Trans A.. Vol. 20A. No. 11. 1989.2249-2458. The nature of interparticle bonding in explosively consolidated. centrifugally atomized (CA). and vacuum gas-atomized (VGA) Type 304 stainless steel powders has been examined. Stress waves with sufficientamplitudeto producefulldensitydo not necessarily produce metallurgical bonds betweenparticles;the localstrain and strain ratearc found to determine the degreeof local heatingand. in tum. the degree of particle fusion. Particle interaction is found to be limited to nearest neighbours. The as- consolidated CA material has approximatelytwicetheultimatetensilestrengthof mill-annealed wrought Type 304 stainless steel. Consolidated CA powder has a higher defect density than VGA powder consolidated under the same conditions; however, the VGA material recrystallizes at a lowertemperaturedue to a lower concentration of carbides. Annealing explosively consolidatedmaterialproducedfromeither powder results in sintering, improved particlebonding.and greater ductility.
Tantalum EfFECT OF Si ON PROPERTIES OF Ta K D Moser. et al, (Cabot Corporation. Boyertown. PA, USA). J Metals (TMS). October1989.50-53. Themicroalloying oftantalumwith silicon hasbeen effectively used on a commercial scale. However,
K Majima, J. Japan Soc. Powder and Powder Metallurgy. Vol. 36.No.8.1989. 41-49. In Japanese. The effectofcutcctoid ~ stabilizingclementson the sinteringcharacteristics ofTi powdercompacts was carried out in order to get the high dense sintercd Ti alloy by the conventional sinlering method through a blended elemental process.The addition of Fe. Ni and Co among eutectoid ~ stabilizing clements showed the excellent effect on the densification of Ti powder compacts. where the sintered density ratio of Ti-4 mass% Co specimen washigherthan 99%.and both of theirratiosofTi-4 mass%Fe and Ti- 4 mass%Ni were higher than 98%. The tensile properties for sintered Ti-4 mass%Co and Ti-4 Fe specimens were remarkably improved by (a + ~)-quenching after ~-solution treatment. and the corrosion resistance of Ti-4 mass%Fespecimen in both of physiological saline solution and IN-Hel solution was confinned to be better than those of Ti-6 AI-4 V specimen or Ti-5 AI-2.5Fe specimenwhich was newly developed as implanted material. In addition. the implantation test maintained in the tibia ofrabbit for 14 months showedthatTi-4Fespecimenhad theexcellentbiocompatability.
MICROSTRUCTUREIPROCESSING RELATIONSHIPS INIIIGII·ENERGY IIIGH-RATE CONSOLIDATED PO\\'DER COl\IPOSITES OF l'.'b·STABIUZED TiJAI + TiAI C Persad, et al, (Texas University. Austin. USA). ProceedingofMaterials Research Society.Vol. 133. 1989.717-722. A new approach to powderprocessing is employed in forming titanium alurninide composites. The processingconsistsof internal heating of a powder blend by a fast electrical discharge of 'lMJ in IS'. Pulse permits rapid heating of an electrically conductingpowdermixturein a cold wall die.This short time at temperature approach offers the opportunity to control phase transformations and the degreeofmicrostructural coarseningnot readily possible with standard powder processing approaches.This paperdescribesthe consolidation results of titanium aluminide- based powder compositematerials. Thefocusofthis study wasthe definition of microstructure/processing relationships for each of the composite constituents. first as monoliths and then in composite forms. Non-equilibrium phases present 375