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Magnetic properties of neodymium-iron-boron sintered from granulated powders
of drilling parameters and alloy composition, including machining enhancers and resin impregnation. Resin impregnation gave the greatest improvement in machinability followed by MnS. Some alloys, notably stainless steels, proved difficult to machine without impregnation. CHANGE OF DENSITY IN COLD DEFORMED SINTERED STEEL J.Lukowski, MSkura. (Slaska Polytechnic, Katowice, Poland.) Rudy Metale, Vol43, No 51998,248253. (In Polish.) An investigation to determine optimum conditions for production of defectfree sintered steel, with density increased by cold forming, is described. Choice of cold forming method is considered. DIFFUSION OF FERROUS COMPACTS DURING SINTERING K.Asaka, T.Kagaya. (Hitachi Powdered Metals Co Ltd, Matsudo, Japan.) J. Jpn Sot. Powder Powder Metal, Vol 44, No 8,1997,751-756. (In Japanese.) Diffusion bonding in stainless steel compacts during sintering was investigated. Corrosion resistance is reduced by C so Ni and Cu were added to aid diffusion bonding. A part consisting of 304L-2%Cu and 304L sub-parts is considered to be a suitable combination of alloys. The interface is shown to be well diffused. Twins were observed in the microstructures. EFFECT OF SINTERING CONDITIONS AND ADDITION OF MOLYBDENUM ON SINTERING OF COARSE IRON POWDER S.Unami, K.Hayashi. (University of Tokyo, Tokyo, Japan.) J. Jpn Sot. Powder Powder Metall., Vol 44, No 8, 1997, 765 769. (In Japanese.) It is reported that the addition of 2 to 4wt%Mo to coarse Fe powder enhances densification during sintering. Densities of 96 to 98% were attained in solid phase sintered Fe-MO at 1300°C for 1 to 4 hours. Without MO, Fe showed little densification.
Molybdenum SINTERING OF MOLYBDENUM POWDER COMPACTS BY SPARE PLASMA SINTERING T.Sakamoto. (Yatsushiro College of Technology, Yatsushiro, Japan.) J. Jpn Sot. Powder Powder Metal, Vol 44, No 9,1997,845-850. (In English.) Compacts of MO powder and of MO powder with Ni added as a sintering enhancer were processed by spark plasma sintering. The process is shown to be effective for MO and Mo-Ni but there
36 MPR February 1999
was excessive grain growth after longer sintering times. Mo-Ni densified more rapidly than MO. Ni reduced the activation energy for sintering.
Ceramic
.materials
CERMETS PREPARED FROM ALUMINA POWDER COATED WITH TITANIUM NITRIDE AND NICKEL S.Li et al. (Beijing University of Aeronautics and Astronautics, Beijing, China.) Znt. J. Refractory Metals Hard Mater., Vol 16, No 2, 1998119-126. A study, intended to improve A&O,Ni cermets by coating the Al,O, with TIN, is described. Powder mixtures were hot pressed to form the Al,O,ITiN-Ni cermets. Density was reduced by increase in %Al,O, and increased by finer particles. Mechanical properties were determined and were higher for the fine grained materials, 10 to 20 pm, than those of coarse grain, 40 to 50 pm. Mechanical properties, except hardness, were reduced by increase in Al,O, content. NON-SHRINKING ALUMINA MATERIALS SHarada et al. (Matsushita Electronic Components Co Ltd, Kadoma, Japan.) J. Jpn Sot. Powder Powder Metall., Vo144, No 8, 1997,729-733. (In Japanese.) A study of shaping, sintering and oxidation of Al,O,-Al materials is described. The object was to minimize shrinkage during processing. Compacts were pressed at 190 MPa and sintered in air at 1600°C. The Al oxidized above 450°C and some Al exuded from the surface of the compacts. The oxidation of Al counteracts shrinkage. MgO, CaCO, and TiO, were added to minimize loss of Al, and Si was added to oppose shrinkage above 1400°C. Sintered A&O,, with a density of 3.72 g.cmm3and 0.7% shrinkage, was produced. The structures contained mullite. FRACTURE OF ZIRCONIA THERMAL BARRIER COATINGS UNDER THERMAL FATIGUE R.Watanabe et al. (Tohoku University, Sendai, Japan.) J. Jpn Sot. Powder Powder Metal, Vol 44, No 8, 1997, 734739. (In Japanese.) Spalling of thermally sprayed ZrO,Y,O, coatings on a Ni-Cr-AI-Y coated stainless steel substrate was investigated during rapid thermal cycling, to simulate service conditions. Acoustic emission signals were used to detect initiation of cracks. The mechanism of spalling is discussed. The sequence is shown to be formation of cracks through the coating, then at the interface followed by detachment of the coating.
Hectrical materials
and magnetic
ENHANCEMENT OF DENSIFICATION OF IRON NITRIDE IN LIQUID PHASE SINTERING BY ADDITION OF ZINC S.Unami, K.Hayashi. (University of Tokyo, Tokyo, Japan.) J. Jpn Sot. Powder Powder Metall., Vol 44, No 8, 1997, 757764. (In Japanese.) A study of the effects of Zn on pressureless liquid phase sintering of Fe,N, to overcome the instability of Fe,N by lowering the sintering temperature, is described. Fe,N-lO%Zn powder was heat treated in H at 43O”C, mixed with a further 20%Zn powder, compacted and sintered to a density of 84%. The heat treated powder contained a FeZn phase on the Fe,N particle surfaces which was readily wetted by the additional Zn during sintering at 550°C. Fe,N has high saturation magnetization. MAGNETIC PROPERTIES OF NEODYMIUM-IRON-BORON SINTERED FROM G-TED POWDERS YKishimoto, O.Yamashita. (Sumitomo Special Metals Co Ltd, Osaka, Japan.) J. Jpn Sot. Powder Powder Metal, Vo144, No 8,1997,775-780. (In Japanese.) It is reported that Nd-Fe-B magnets had been prepared from powder granulated by a spray drying technique using a polymer binder. Magnetic properties are described. CHARACTERISTICS OF FORMING BONDED MAGNET POWDERS BY ULTRASONIC VIBRATION SMino et al. (Sumitomo Special Metals Co Ltd, Osaka, Japan.) J. Jpn Sot. Powder Powder Metall., Vol 44, NO 9, 1997,807-811. (In Japanese.) A study of the effects of oriented ultrasonic vibration on consolidation of anisotropic Nd-Fe-B magnetic powder, with an epoxy resin binder, is described. The applied vibration was shown to be sufficient to melt the binder and effects of process parameters were investigated. The technique is shown to reduce process times and temperatures.
Hard materials steels
and tool
CARBON NITRIDE J.Hofmann. (PRAMET AS, Sumperk, Czech Republic.) Pokroky Praskove Metal., Vo135, No 4,1997,5-20. (In Czech.) Recent literature concerning a new superhard material, carbon nitride, is reviewed with reference to production, properties and potential applications.
Molybdenum SINTERING OF MOLYBDENUM POWDER COMPACTS BY SPARE PLASMA SINTERING T.Sakamoto. (Yatsushiro College of Technology, Yatsushiro, Japan.) J. Jpn Sot. Powder Powder Metal, Vol 44, No 9,1997,845-850. (In English.) Compacts of MO powder and of MO powder with Ni added as a sintering enhancer were processed by spark plasma sintering. The process is shown to be effective for MO and Mo-Ni but there
36 MPR February 1999
was excessive grain growth after longer sintering times. Mo-Ni densified more rapidly than MO. Ni reduced the activation energy for sintering.
Ceramic
.materials
CERMETS PREPARED FROM ALUMINA POWDER COATED WITH TITANIUM NITRIDE AND NICKEL S.Li et al. (Beijing University of Aeronautics and Astronautics, Beijing, China.) Znt. J. Refractory Metals Hard Mater., Vol 16, No 2, 1998119-126. A study, intended to improve A&O,Ni cermets by coating the Al,O, with TIN, is described. Powder mixtures were hot pressed to form the Al,O,ITiN-Ni cermets. Density was reduced by increase in %Al,O, and increased by finer particles. Mechanical properties were determined and were higher for the fine grained materials, 10 to 20 pm, than those of coarse grain, 40 to 50 pm. Mechanical properties, except hardness, were reduced by increase in Al,O, content. NON-SHRINKING ALUMINA MATERIALS SHarada et al. (Matsushita Electronic Components Co Ltd, Kadoma, Japan.) J. Jpn Sot. Powder Powder Metall., Vo144, No 8, 1997,729-733. (In Japanese.) A study of shaping, sintering and oxidation of Al,O,-Al materials is described. The object was to minimize shrinkage during processing. Compacts were pressed at 190 MPa and sintered in air at 1600°C. The Al oxidized above 450°C and some Al exuded from the surface of the compacts. The oxidation of Al counteracts shrinkage. MgO, CaCO, and TiO, were added to minimize loss of Al, and Si was added to oppose shrinkage above 1400°C. Sintered A&O,, with a density of 3.72 g.cmm3and 0.7% shrinkage, was produced. The structures contained mullite. FRACTURE OF ZIRCONIA THERMAL BARRIER COATINGS UNDER THERMAL FATIGUE R.Watanabe et al. (Tohoku University, Sendai, Japan.) J. Jpn Sot. Powder Powder Metal, Vol 44, No 8, 1997, 734739. (In Japanese.) Spalling of thermally sprayed ZrO,Y,O, coatings on a Ni-Cr-AI-Y coated stainless steel substrate was investigated during rapid thermal cycling, to simulate service conditions. Acoustic emission signals were used to detect initiation of cracks. The mechanism of spalling is discussed. The sequence is shown to be formation of cracks through the coating, then at the interface followed by detachment of the coating.
Hectrical materials
and magnetic
ENHANCEMENT OF DENSIFICATION OF IRON NITRIDE IN LIQUID PHASE SINTERING BY ADDITION OF ZINC S.Unami, K.Hayashi. (University of Tokyo, Tokyo, Japan.) J. Jpn Sot. Powder Powder Metall., Vol 44, No 8, 1997, 757764. (In Japanese.) A study of the effects of Zn on pressureless liquid phase sintering of Fe,N, to overcome the instability of Fe,N by lowering the sintering temperature, is described. Fe,N-lO%Zn powder was heat treated in H at 43O”C, mixed with a further 20%Zn powder, compacted and sintered to a density of 84%. The heat treated powder contained a FeZn phase on the Fe,N particle surfaces which was readily wetted by the additional Zn during sintering at 550°C. Fe,N has high saturation magnetization. MAGNETIC PROPERTIES OF NEODYMIUM-IRON-BORON SINTERED FROM G-TED POWDERS YKishimoto, O.Yamashita. (Sumitomo Special Metals Co Ltd, Osaka, Japan.) J. Jpn Sot. Powder Powder Metal, Vo144, No 8,1997,775-780. (In Japanese.) It is reported that Nd-Fe-B magnets had been prepared from powder granulated by a spray drying technique using a polymer binder. Magnetic properties are described. CHARACTERISTICS OF FORMING BONDED MAGNET POWDERS BY ULTRASONIC VIBRATION SMino et al. (Sumitomo Special Metals Co Ltd, Osaka, Japan.) J. Jpn Sot. Powder Powder Metall., Vol 44, NO 9, 1997,807-811. (In Japanese.) A study of the effects of oriented ultrasonic vibration on consolidation of anisotropic Nd-Fe-B magnetic powder, with an epoxy resin binder, is described. The applied vibration was shown to be sufficient to melt the binder and effects of process parameters were investigated. The technique is shown to reduce process times and temperatures.
Hard materials steels
and tool
CARBON NITRIDE J.Hofmann. (PRAMET AS, Sumperk, Czech Republic.) Pokroky Praskove Metal., Vo135, No 4,1997,5-20. (In Czech.) Recent literature concerning a new superhard material, carbon nitride, is reviewed with reference to production, properties and potential applications.