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Effect of bubbles on abnormal grain growth in PM fine tungsten wires
Powder production MANUFACTURE OF COPPER POWDER FROM COPPER SCALE J.Lezanski et al. (Academia Gornicza-Hutnicza, Krakow, Poland.) Metal. fioszkcow; Vol 29, No 3, 1996, 3-9. (In Polish.) The first stage in the hydrometallurgical processing of Cu oxide scale into Cu powder is outlined. The scale is dissolved in acid and precipitated. The characteristics of the powder are described and mechanisms discussed.
Fundamentals METHOD FOR ASSESSMENT OF POWDER PACKING DURING POWDER FORMING J.J.Reddy. (Defence Metallurgical Research Laboratory, Hyderabad, India.) Powder Metall., Vol 39, No 4, 1996, 281-285. Packing of powder is discussed and it is noted that estimates of packing from powder characteristics are erratic owing to interparticle friction. It is reported that the use of a wetting fluid avoids friction and allows particle rearrangement but requires costly equipment for monitoring. A method of assessment by measurement of temperature rise during mixing is suggested and measurements are described. Effects of powder and process parameters on the assessment are discussed. EFFECT OF PROCESSING ON CAPILLARITY OF POROUS PM MATERIALS V.B.Savich. Poroshkovaya Me1996, 30-38. (In Russian.) Characteristics of infiltration in Fe, Cu and Ti alloys are described with regard to effects of process parameters. Greatest penetration is found with the smallest pores. Control of pore size, with variable sizes, by use of controlled powder size distribution, sintering of oxidized powder, foaming agents and precoating of base powder is discussed.
VKShelekh,
tall, No5/6,
DEVELOPMENT OF CIRCULATION CELL STRUCTURES IN GRANULAR MATERIALS UNDER COMPRESSION .J.R.Williams, N.Rege. (Massachusetts Inst. of Technology, Cambridge, USA.) &rrder Technol., Vol 90, No 3, 1997, 187-194. Formation of microstructures in granular material undergoing compression
38 MPR November 1997
is predicted for particles of differing shapes and sizes, There is deviation from the prediction of continuum theory in that localized structures (circulation cells) are formed in which particles behave as a rigid body. The cells can migrate and coalesce to form a larger structure. Shear bands form at boundaries between cells.
Aluminium DEGASSING OF GAS ATOMIZED ALUMINIUM-LITHIUM BASE ALLOY POWDERS S.J.Davis et al. (University of Surrey, Guildford. UK.) Int. J. Rapid Solidjfjcation, Vol 9, No 3. 1996, 211-240.
Surfaces of as-gas atomized and asdegassed A1-Li base alloy powders were investigated. AlzO:i was thicker on AI-Li than on pure Al and thickness increased with particle size. II was present as LiH or LiOH. LiH transformed to LiOH in presence of moisture. It is proposed that the surface layer consists of LiOHILi,CO:~iAl,O:~ with mixed oxides and metal.
Magnesium INFLUENCE OF CONSOLIDATION STAGE ON PROPERTIES OF MAGNESIUM-ALUMINIUM-ZINC ALLOYS D.Daloz. G.Michot. (Ecole des Mines, Nancy, France.) Int. J. Rapid Solidification, Vol 9, No 4, 1996, 289-304. It is reported that two Mg-A-Zn alloys had been made by centrifugal atomization and consolidated by extrusion, dynamic recrystallization occurring in the die. Grain sizes of 0.2 to 1.0 pm were attained with a yield stress of 500 MPa. Effects of extrusion speed and temperatures were determined. The high yield stress is attributed to grain boundary effects. Low ram speed and extrusion temperature gave highest strength owing to finest grain size and limitation of grain growth. Alloy level should be below 15% for ductility.
Tungsten EFFECTOFBUBBLESONABNORMAL GRAIN GROWTH IN PM FINE TUNGSTEN WIRES
CREEP OF PM 2024 ALUMINIUM ALLOY E.Cerri et al. (University of Ancona. Ancona, Italy.) Acta IMater., Vol 45, No 2, 1997, 529-540. Creep at 250 to 310°C of PM 2024Al alloy was investigated. A short quasi-steady state condition and a long tertiary stage were found. Stress exponent is reported to be high and variable with a large activation energy. Before testing structures contained CL& and CuMgAl, particles. Fine particles were precipitated during testing. Analysis of data used a threshold stress in the creep equation and the importance of this is discussed. CRYSTALLIZATION PROCESSES IN AMORPHOUS ALUMINIUM AND IRON BASE ALLOYS HFujita et al. (Kinki University, Osaka, *Japan.) J. Japan Inst. Metals, Vol 60, No 11, 1996, 1031-1036. (In Japanese.) Crystallization of Al and Fe base alloys was investigated by electron microscopy. It is reported that there is a constant nucleus size. Lattice parameters change progressively until completion of recrystallization. Grain size stabilized at 10 nm until secondary phases are precipitated. Grain size reaches 50 to 100 nm at higher temperatures.
K.Tanoue, KFuruta. (Kyushi Inst. of Technoloo, Kitakyushi, Japan.) J. Japan Inst. Metals, Vol 60, No 11, 1996, 1064-1071. (In Japanese.) The relationship between grain shape and ambient temperature grain boundary fracture in fine W wires is discussed with reference to the amount and distribution of bubbles. A computer Monte Carlo simulation of abnormal grain growth is described. It is shown that some nuclei survive and others vanish; the largest grains increase in size as the numbers of nuclei diminish. Abnormal grain growth is accelerated when primary grain growth is inhibited. It is concluded that abnormal grain structure develops when boundaries break away from arrays of bubbles. GRAVITATIONAL EFFECTS ON GRAIN COARSENING DURING LIQUID PHASE SINTERING R.M.German et al. (Pennsylvania State University, Pennsylvania, USA.) Metall. Mater. 7?ans A, Vol 28A, No 1, 1997, 215221. Grain growth in liquid phase sintering is discussed with reference to Ostwald ripening, grain contact in high solid content alloys, coalescence and conflict with other theories. It is noted that observed and predicted growth rates differ
Fundamentals METHOD FOR ASSESSMENT OF POWDER PACKING DURING POWDER FORMING J.J.Reddy. (Defence Metallurgical Research Laboratory, Hyderabad, India.) Powder Metall., Vol 39, No 4, 1996, 281-285. Packing of powder is discussed and it is noted that estimates of packing from powder characteristics are erratic owing to interparticle friction. It is reported that the use of a wetting fluid avoids friction and allows particle rearrangement but requires costly equipment for monitoring. A method of assessment by measurement of temperature rise during mixing is suggested and measurements are described. Effects of powder and process parameters on the assessment are discussed. EFFECT OF PROCESSING ON CAPILLARITY OF POROUS PM MATERIALS V.B.Savich. Poroshkovaya Me1996, 30-38. (In Russian.) Characteristics of infiltration in Fe, Cu and Ti alloys are described with regard to effects of process parameters. Greatest penetration is found with the smallest pores. Control of pore size, with variable sizes, by use of controlled powder size distribution, sintering of oxidized powder, foaming agents and precoating of base powder is discussed.
VKShelekh,
tall, No5/6,
DEVELOPMENT OF CIRCULATION CELL STRUCTURES IN GRANULAR MATERIALS UNDER COMPRESSION .J.R.Williams, N.Rege. (Massachusetts Inst. of Technology, Cambridge, USA.) &rrder Technol., Vol 90, No 3, 1997, 187-194. Formation of microstructures in granular material undergoing compression
38 MPR November 1997
is predicted for particles of differing shapes and sizes, There is deviation from the prediction of continuum theory in that localized structures (circulation cells) are formed in which particles behave as a rigid body. The cells can migrate and coalesce to form a larger structure. Shear bands form at boundaries between cells.
Aluminium DEGASSING OF GAS ATOMIZED ALUMINIUM-LITHIUM BASE ALLOY POWDERS S.J.Davis et al. (University of Surrey, Guildford. UK.) Int. J. Rapid Solidjfjcation, Vol 9, No 3. 1996, 211-240.
Surfaces of as-gas atomized and asdegassed A1-Li base alloy powders were investigated. AlzO:i was thicker on AI-Li than on pure Al and thickness increased with particle size. II was present as LiH or LiOH. LiH transformed to LiOH in presence of moisture. It is proposed that the surface layer consists of LiOHILi,CO:~iAl,O:~ with mixed oxides and metal.
Magnesium INFLUENCE OF CONSOLIDATION STAGE ON PROPERTIES OF MAGNESIUM-ALUMINIUM-ZINC ALLOYS D.Daloz. G.Michot. (Ecole des Mines, Nancy, France.) Int. J. Rapid Solidification, Vol 9, No 4, 1996, 289-304. It is reported that two Mg-A-Zn alloys had been made by centrifugal atomization and consolidated by extrusion, dynamic recrystallization occurring in the die. Grain sizes of 0.2 to 1.0 pm were attained with a yield stress of 500 MPa. Effects of extrusion speed and temperatures were determined. The high yield stress is attributed to grain boundary effects. Low ram speed and extrusion temperature gave highest strength owing to finest grain size and limitation of grain growth. Alloy level should be below 15% for ductility.
Tungsten EFFECTOFBUBBLESONABNORMAL GRAIN GROWTH IN PM FINE TUNGSTEN WIRES
CREEP OF PM 2024 ALUMINIUM ALLOY E.Cerri et al. (University of Ancona. Ancona, Italy.) Acta IMater., Vol 45, No 2, 1997, 529-540. Creep at 250 to 310°C of PM 2024Al alloy was investigated. A short quasi-steady state condition and a long tertiary stage were found. Stress exponent is reported to be high and variable with a large activation energy. Before testing structures contained CL& and CuMgAl, particles. Fine particles were precipitated during testing. Analysis of data used a threshold stress in the creep equation and the importance of this is discussed. CRYSTALLIZATION PROCESSES IN AMORPHOUS ALUMINIUM AND IRON BASE ALLOYS HFujita et al. (Kinki University, Osaka, *Japan.) J. Japan Inst. Metals, Vol 60, No 11, 1996, 1031-1036. (In Japanese.) Crystallization of Al and Fe base alloys was investigated by electron microscopy. It is reported that there is a constant nucleus size. Lattice parameters change progressively until completion of recrystallization. Grain size stabilized at 10 nm until secondary phases are precipitated. Grain size reaches 50 to 100 nm at higher temperatures.
K.Tanoue, KFuruta. (Kyushi Inst. of Technoloo, Kitakyushi, Japan.) J. Japan Inst. Metals, Vol 60, No 11, 1996, 1064-1071. (In Japanese.) The relationship between grain shape and ambient temperature grain boundary fracture in fine W wires is discussed with reference to the amount and distribution of bubbles. A computer Monte Carlo simulation of abnormal grain growth is described. It is shown that some nuclei survive and others vanish; the largest grains increase in size as the numbers of nuclei diminish. Abnormal grain growth is accelerated when primary grain growth is inhibited. It is concluded that abnormal grain structure develops when boundaries break away from arrays of bubbles. GRAVITATIONAL EFFECTS ON GRAIN COARSENING DURING LIQUID PHASE SINTERING R.M.German et al. (Pennsylvania State University, Pennsylvania, USA.) Metall. Mater. 7?ans A, Vol 28A, No 1, 1997, 215221. Grain growth in liquid phase sintering is discussed with reference to Ostwald ripening, grain contact in high solid content alloys, coalescence and conflict with other theories. It is noted that observed and predicted growth rates differ