Effect of porosity on properties of gas nitrided sintered iron

Effect of porosity on properties of gas nitrided sintered iron

Powder production PRODUCTION OF UNIFORM SPHERICAL BISMUTH-ANTIMONY PARTICLES FOR THERMO-ELECTRIC DEVICES A.Kawasaki et al. (Tohoku University, Send...

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PRODUCTION OF UNIFORM SPHERICAL BISMUTH-ANTIMONY PARTICLES FOR THERMO-ELECTRIC DEVICES

A.Kawasaki et al. (Tohoku University, Sendai, Japan.) J. Jpn Sot. Powder Powder Metall., Vol 44, No 7, 1997, 700706. (In Japanese.) It is reported that 200 pm uniform Bi-lB%Sb powders had been prepared by pulsed orifice injection. The powders were spherical with some segregated pure Bi and a 100 nm oxide film on the surface.

Pressing EFFECT OF LUBRICATION MODE AND COMPACTION TEMPERATURE ON PROPERTIES OF ALLOY STEEL

RMGerman et al. (Pennsylvania State University, Pennsylvania, USA.) Znt. J. Powder Mrtail., Vol 34, No 2, 1998, 29-33. Relationships between green and sintered densities are discussed with consideration of improvements in part properties. Means of increasing green density, including warm compaction and elimination of admixed lubricants, are reviewed. An investigation of two compaction temperatures and three PTFE lubrication techniques, using Fe-2%Ni2%Cu-0.85%Mo-0.8%C, is described. Experimental conditions were evaluated in terms of green and sintered properties. The best combination of green and sintered properties was attained with cold compaction and dry admixed lubricant compared with powder coating, die wall lubrication and warm compaction.

Iron and steel SILICIDE PHASE FORMATION AND EFFECT ON LIQUID PHASE SINTERING OF STAINLESS STEEL

J.D.Bolton et al. (University of Bradford, Bradford, UK. I Powder Metall., Vol 41, No Z&1998,93-101. Addition of elemental Si to 316L stainless steel was investigated. Liquid phases are reported to form at 1060 and 1155”C, due to reaction of Si with steel, resulting in formation of silicide phases with Fe, Cr and Ni. A further silicide formed on exceeding the solidus temperature at 1190°C. The steel did

not densify fully due to voids at reaction sites from which the liquid phase drained away by capillary action and which were not filled by supersolidus sintering above 1200°C. Interconnected porosity was at a low level after sintering at 1250 to 1300°C. It is suggested that the alloy may have good corrosion resistance.

Sec. Powder Powder Metall., Vol 44, No 7,1997,689-693. (In English.) It is shown that the addition of Ni to MO powder increases sintered density and reduces sintering activation energy. 2% Ni gave a density of 94%. Addition of Ni-Fe increased density to 98.5% on sintering at 1400°C in Mo-5%(Ni-20%Fe) alloy. Ni-Cr acted in a similar manner.

MACHINABILITY AND OXIDATION RESISTANCE OF PM STEEL WITH MODIFIED MANGANESE SULPHIDE ADDITIONS

Silver

K.S.Chopra, S.F.Claeys. (Pyron Corp, New York, USA.) Int. J. Powder Metall., Vol 34, No 2,1998, 29-36. The usefulness of MnS for enhancement of machinability of steels is discussed. Residual porosity in the steel limits tool life and restricts use of liquid coolants. A study, aimed at improving machinability of PM steel by use of MnS, with a controlled addition of Fe, IS described. Shortcomings of pure MnS are reviewed. For the modified MnS, 0 content, particle size distribution and Fe are analysed. The modified MnS is reported to enhance machinability and to improve oxidation resistance compared with pure MnS. EFFECT OF POROSITY ON PROPERTIES OF GAS NITRIDED SINTERED IRON

A.Salek et al. (Slovak Academy of Sciences, Kosice, Slovak Republic.) Pokroky Praskove Metal., Vol 35, No 3, 1997,42-52. (In English.) An investigation of the effects of porosity, 1.6 to 84%, on gas nitriding of sintered Fe is described. Structure, hardness, dimensional changes and amount of absorbed N were studied. It is shown that 10% porosity is the maximum at which the E-phase is formed. When formed this phase is similar to that formed in wrought steel. Above 10% porosity deep penetration of N into the Fe prevents formation of the c-phase. Thickness of the E-phase can be controlled through porosity and process parameters.

Molybdenum EFFECTS OF NICKEL IRON AND CHROMIUM ON SINTERING OF MOLYBDENUM POWDERS

T.Sakamoto. (Yatsushiro College of Technology, Yatsushiro, Japan.) J. Jpn

MICROSTRUCTURE OF SINTERED SILVER-NICKEL ALLOYS

SGacek. (Akademia Gorniczo-Hutnicza, Krakow, Poland.) Rudy Metale, Vol 43, No 4, 1998, 190- 195. (In Polish.) The effects of green density and sintering time on density of sintered Ag20%Ni alloys were investigated. Two Ag powders, differing in particle size and morphology, were used. Structural evolution was studied.

Titanium PREPARATION OF TITANIUM-IRON HYDROGEN STORAGE ALLOY IN MICROGRAVITlr

H.Suzuki et al. (Hokkaido National Industrial Research Inst., Sapporo, Japan.) J. Jpn Sot. Powder Powder Metall., Vol 44, No 7, 1997, 641-646. (In Japanese.) Use of Ti-.Fe as a storage alloy for H was noted with the need for a homogeneous structure and a large surface area. Effects of microgravity on preparation of the alloy from powders was investigated with regard to absorption/desorption reactions. Processing in microgravity is reported to result in a more homogeneous structure. Microgravity processed materials did not show powdering after cyclic H absorption/desorption reactions. ROLE OF HYDROGEN DURING PLASMA NITRIDING OF TITANIUM M.Tamaki et’ al. (Kyoto University, Kyoto, Japan.) J. Jpn Sot. Powder Powder Metall., Vol 44, No 7, 1997, 712715. (In Japanese.) Plasma nitriding of Ti in N-H was investigated. H is shown to enhance nitride formation. The effect is great,est at SOvol%H. The effect is attributed to the presence of XH radicals. Nitride layers contained TiN and T&N. The microstructure showed an acicular texture.

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