PM SINTERING AND MICROSTRUCTURE OF P H O S P H O R U S S T E E L S
A. Molinari et al (University of Trento, Italy), Powder Metallurgy, Vol 35, No 4, 1992, 285-291. A study of microstructural development and sintering mechanism in nine Fe-C-P steels with 0.25, 0.5 or 0.7 wt% C and 0.45, 0.6 or 0.8 wt%P is described. Thermal analysis, secondary ion mass spectroscopy and metallography were used. Increase of C and P enhanced pore spheroidization, P is shown to be unequally partitioned between f e r r i t e a n d p e a r l i t e . The r e s u l t s are d i s c u s s e d in t e r m s of two s i n t e r i n g mechanisms. Firstly, formation of P-rich ferrite by reaction between phosphide and low phosphorus austenite and, secondly, the formation of a transient liquid phase of reaction between phosphide and C-rich austenite. The relative importance of the two mechanisms is found to depend on alloy composition. D E N S I F I C A T I O N OF P O R O U S ALLOY STEEL D U R I N G HOT U P S E T T I N G
K.T. Kim et al (Pohang Inst of Science and Technology, Korea), J Korean Inst of Metals, Vol 30, No 5, 1992, 574-578. (In Korean). T h e r m o - v i s c o p l a s t i c r e s p o n s e and d e n s i f i c a t i o n of p o r o u s a l l o y s t e e l preforms under conditions of hot compression were investigated. The density distributions are derived from the relationships between Rockwell hardness and relative density.
C H A N G E S IN D I S T R I B U T I O N O F ALLOY E L E M E N T S D U R I N G S I N T E R I N G OF D I F F U S I O N ALLOYED S T E E L
T. Mickiewicz and M. Czepelak (Inst Metali Niezelaznych, Gliwice, Poland), Metal Proszkow, Vol 25, No 3, 1992, 101-106. (In Polish). Changes in the distribution of alloy e l e m e n t s d u r i n g sintering of diffusion alloyed steel powders were investigated by microscopy and X-ray techniques. The alloy e l e m e n t s a r e r e p o r t e d to be m o r e homogeneously distributed after sintering. A Cu-Ni phase was reported to exist in some specimens of powder and sintered compacts.
HOT D E N S I F I C A T I O N OF S I N T E R E D STEELS
G. Modzelewska (Inst Metali Niezelaznych, Gliwice, Poland), Metal Proszkow, Vol 25, No 3, 1992,107-109. (In Polish). The p a p e r describes densification of sintered steel c o m p a c t s in screw and rotary forging presses. Steels of a range of compositions were studied.
MPR May 1993
F O R M A T I O N O F IRON S I L I C I D E S A N D SILICON CARBIDE BY MECHANICAL ALLOYING
T. Tanaka et al (Osaka Sangyo University, Daito, Japan), J Japan Soc Powder and Powder Metallurgy, Vol 39, No 10, 1992, 865-869. (In Japanese). A study of the MA of Fe-Si-C powders in a ball mill, under Ar and phase evolution is described. It is shown that Si suppresses the formation of Fe carbides and promotes amorphization. At high %Si FeSi, ~ F e S i 2 and SiC, after partial amorphization, are reported to be formed. The process is said to be typical of metal/non-metal systems.
I N F L U E N C E OF ALUMINA INCLUSIONS ON S I N T E R I N G OF SUPERALLOY POWDERS M. Lafer et al (UJF/CRNS/INPG, Grenoble, France), Powder Metall Int, Vol 25, No 1, 1993, 23-27. Densification of a Ni-based superalloy containing A1203 was investigated. The powder m i x t u r e s were consolidated by HIP. HIP kinetics were deduced from the microstructures of i n t e r r u p t e d HIP specimens. Hot compression tests were c a r r i e d o u t on d e n s e s p e c i m e n s . An explanation of the effect of the A1203 inclusions in retarding densification is suggested.
of ball wear debris. It is reported that Fe from steel balls enters the Ni phase and the A1203 is present as dispersoids. Solution of W in Ni is not affected by wear debris and amounts of W in excess of equilibrium solubility were detected. Ni amorphizes when %Ni e x c e e d s 28 a t % . T h e a m o r p h i z e d p h a s e r e c r y s t a l l i z e d on heating to 725°C and the phases present are then reported to be mainly Ni4W and NiW.
C O M P O S I T E CONTACT MATERIALS M A D E BY HYDOSTATIC E X T R U S I O N OF S I N T E R E D METALS
K. Wojasik and S. Stolarz (Inst Metall Niezelaznych, Gliwice, Poland), Metal Proszkow, Vol 25, No 3, 1992, 96-100. (In Polish). The effects of deformation on structure of sintered A4~-(10, 20 or 30) % Ni alloys was investigated. The alloys were hydrostatically extruded and drawn into wire with up to 90% d e f o r m a t i o n . T h e r e l a t i o n s h i p s between amount of deformation and %Ni and properties are shown and the use of the m a t e r i a l s f o r e l e c t r i c a l c o n t a c t s is suggested.
S T R U C T U R E OF P R O P E R T I E S OF T H E B O N D E D A R E A IN A J O I N T B E T W E E N S T E E L A N D A SUPERALLOY
EFFECTS OF PRESSURE OF CRYSTALLIZATION O F A M O R P H O U S TITANIUM-COPPER ALLOYS
E.P. Kratt et al (NPO VILS, Moscow, Russia), Powder Metall Int, Vol 25, No 1, 1993, 28-30. The application of a superalloy coating, applied to a steel substrate is described the o b j e c t b e i n g to p r o v i d e a w e a r and corrosion resistant surface. The structure and strength of the bonded interface were i n v e s t i g a t e d a n d are d e s c r i b e d . It is reported that the bond strength is not lower than that of the steel substrate. Fracture is found to be initiated at second phase particles which contained A1, O and C and were located at the coating/substrate interface. The fracture then propagated into steel.
T. Morooka et al (Musashi Inst of Technology, Tokyo, Japan), J Japan Soc Powder and Powder Metallurgy, Vol 39, No I0, 1992, 879-883. (In Japanese). The p r o d u c t i o n of a m o r p h o u s Ti43 at% Cu by m e c h a n i c a l alloying is described. It is reported t h a t increase in pressure during sintering increased the recrystallization t e m p e r a t u r e by a b o u t 38°C/GPa.
T U N G S T E N SOLUTION K I N E T I C S A N D A M O R P H I Z A T I O N O F NICKEL IN MECHANICALLY ALLOYED NICKEI~ T U N G S T E N ALLOYS A.O. Aning et al (University of Virginia, Charlottesville, Virginia, USA), Acta MetaU Mater, Vol 41, No 1, 1993, 165-174. The MA of Ni-W alloys in mills with steel or A1203 balls was investigated with regard to amorphization of the Ni and the effects
POWDER METALLURGY OF TITANIUMALUMINIUM-NIOBIUM ALLOYS
L Tao et al (North-West Inst for NonFerrous Metals Research, Baoji, China), Rare Metal Materials and Engineering, Vol 21, No 3, 1992, 53-58. (In Chinese). The effects of HIP parameters and heat treatment on the structure and properties of Ti-14% A1-21% Nb were investigated. The alloy powders were made by the plasma rotating electrode process. The structure is shown to consist of the ~.2 and ~ phases, the volume fraction of ~.2 decreasing with increase in the HIP temperature. Optimum strength and ductility were reported for HIP at I100°C