Hot pressing of titanium aluminide from elemental powders

K.Funami et al. (Chiba Inst. of Technology, Narashino, Japan.) J. Jpn Inst. Metals, Vol 60, No 11, 1996, 1116-1124. (In Japanese.) Oxidation of TiAl-(1 to 5)at%Nb was investigated. Specimens were made by sintering and some were further densitied by HIP. Oxidation was at 925°C in air. Nb and HIP are reported to inhibit oxidation and early spalling of the oxide scale. With 4 and 5%Nb oxidation resistance was good. The scale structure is layered with oxides and nitrides of Ti and Al. PROCESSING

OF IRON ALUMINIDES

BY MECHANICAL

ALLOYING

PLASMA ACTIVATED

AND

SINTERING

K.Yamazaki et al. (University of California, California, USA.) Mater. Sci. Eng. A, Vol207, No 2, 1996, 153-158. High and low energy MA was used to make FesAl from elemental powders. Nano- and fine crystalline powders were compared for effects of milling energy. Consolidation of powder was by plasma activated sintering. Structural evolution of fine and nano-powders were compared. The high energy milled powder alloyed completely into an Fe,Al nanocrystalline solid which differed from the product made from low energy milled powder. PREPARATION ALUMINIDE

OF NIOBIUM

POWDER BY

HYDRIDE-DEHYDRIDE

PROCESS

K.Ohsaki et al. (Nisshin Steel, Japan.) J, Alloy. Compd, Vol 238, No 112, 1996, 202-209. Preparation of NbsAl powder by hydrogenation and dehydrogenation is described. This causes disintegration of particles of NbsAl. A range of compositions were investigated. Structural changes were monitored. It is shown that 14 pm single phase NbsAl powders can be made, in the vacuum melting chamber, with 22 to 28at%Al, without exposure to air. HOT PRESSING ALUMINIDE

OF TITANIUM

FROM ELEMENTAL

POWDERS

J.B.Yang et al. (National Cheng Kung University, Taiwan.) J. Mater. Eng. Performance, Vo15, No 5, 1996, 583-588. The synthesis of Ti aluminides, from elemental powders, during two-stage hot pressing was investigated. It is shown that TiAl, is the first phase to form. As temperature increased, lamellar structures formed in the TiAl, with subsequent transition to TiAl and TisAl. The lamellar structures grew into ring structures between the Ti matrix and T&Al. 42

MPR December

1997

Mechanicalalloying KINETICS AND PHASE TRANSFORMATIONS MECHANICALLY

IN

ALLOYED

ZINC-ALUMINIUM

IRON-

ALLOYS

O.N.C.Uwakweh, Z.Liu (University of Cincinnati, Cincinnati, USA.) Metal. Mater. Trans. A, Vol28A No 3,1997,517-525. Elemental Fe-Zn powders, corresponding to the compositions FesZni,,, Fe,Zn,,, FeZn, and FeZn,, with 5wt%Al were mechanically alloyed in Ar. Phase evolution was investigated by differential scanning calorimetry. In the synthesis of FeZn, and FeZn,,, two diffusion controlled processes were detected with activation energies of 227 and 159 kJ.mol-l. Other reactions were consistent with Fe-Zn-Al phase equilibria for Fe+, Fe+&, and FeZn,. Some revision of the equilibrium phase diagram for Fe-Zn-Al is proposed.

Metal injection OPTIMIZATION MOULDING

Powder Metall., Vol 43, No 1, 1996, 113-117. (In Japanese.) The rheological behaviour of 316L stainless steel MIM feedstocks was investigated for gas and water atomized powders with the object of optimizing the feedstock. It is reported that feedstock viscosity is influenced by powder characteristics, About 2.5wt% additional binder was required for the water atomized powder. The feedstocks exhibited Bingham-type flow properties.

1996 WORLD CONGRESS ON POWDER METALLURGY. The following which

Abstracts are from papers were presented at the which

Congress Washington

was

held

in

DC, USA, in June 1996.

moulding

OF INJECTION

Surface

treatments

PROCESS FOR SILICON

NITRIDE COMPONENTS

PLASMA NITRIDING

D.F.Lii et al. (National Cheng Kung University, Tainan, Taiwan.) Powder Metall., Vol39, No 4, 1996, 291-295. An investigation, with the objective of optimizing the manufacture of Si,N, parts by MIM is described. Effects of feedstock, moulding, debinding and sintering parameters on mechanical properties of parts were studied. The ceramic powder mixture was S&N,-Gwt%Y,O,-2%Al,Os. A model for debinding is proposed. It is reported that complex shaped blades, at a density of 97% with a bend strength of 880 MPa had been produced.

STRENGTH

I.Kuhn et al. (Federal University of St. Catherine, Brazil.1 An investigation of plasma nitriding of sintered high strength low alloy steels was described. The object was to evaluate the effects of process conditions, nitriding time and nitriding atmosphere. Surfaces were characterized. The effect of extent of homogenization during sintering was also assessed.

OPTIMIZATION OF GREEN COMPACT

SURFACES

FORMING

STEEL

STRIJCW AND PROPERTIES OF THIN POWDER LAYERS ON INNER OF BUSHES

IN METAL INJECTION

MOULDING

H.Nomura et al. (Nagoya University, Nagoya, Japan.) J. Jpn Znst. Metals, Vol 60, No 11, 1996,1108-1115. (In Japanese.) MIM is discussed with regard to the unit processes involved. A study aimed at optimization of the injection stage is described, for 304L stainless steel, so that defects are absent and injection is at the lowest possible speed. A numerical analysis for injection is described and good agreement between predicted and experimental findings is reported. RHEOLOGICAL BEHAVIOUR STAINLESS

OF HIGH

SINTERED

OF 316L STEEL PLASTISOLS

M.Asano et al. (Daido Steel Co Ltd, Nagoya, Japan.) J. Jpn Sot. Powder

K.K.Shugay, V.N.Varavka. (Don State Technical University, Russia.) Experiences in the manufacture of composite plain bearings were described. Effects of process and assembly parameters on the working surface were evaluated with regard to the synthesis of intermetallic compounds during sintering of layers added to the working surface. Cooling conditions were investigated for layer adhesion and wear properties.

Lubrication REPLACEMENT OF INTERNAL EXTERNAL LUBRICANTS TRIBOSTATIC DIE WALL LUBRICATION

WITH