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Volume 42, Issue 11
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[in Japanese]1995 Volume 42 Issue 11 Pages 1214
Published: November 15, 1995
Released on J-STAGE: May 22, 2009
JOURNAL OPEN ACCESSDownload PDF (84K) -
Masaharu Tokizane1995 Volume 42 Issue 11 Pages 1215-1222
Published: November 15, 1995
Released on J-STAGE: May 22, 2009
JOURNAL OPEN ACCESSIn the present paper, the author describes the reviews of our recent studies on Ti-rich TiAl intermetallics through two kinds of powder processing routs, plasma rotating electrode process (PREP) and mechanical alloying (MA) process. The HIPed billet of the PREPed powder can be isothermally hot forged to the 78% deformed sound pancake at 950°C and initial strain rate of 3.8×10-4/s by a manner of superplastic hot forging. The pancake consists of γ+α2 microduprex structure, and showed a large elongation to failure value such as 445% by tensile fracture test at 1000°C and initial strain rate of 2.8×10-4/s. From these results, it is presumed that the PREP-HIPed billet can be used as a material for superplastic hot forging to a complicated part. As-HIPed billet of the MA(150hr processed)-powder showed the similar γ+α2 microduplex structure. The results of detailed analysis of high-temperature deformation behavior of this material indicated that, the flow of the material satisfy the condition of fine grain superplasticity controlled by lattice diffusion. It seems to be possible to improve the formability of the intermetallics in the other alloy systems by controlling the structure as has been done in the present case of Ti-rich TiAl alloys.View full abstractDownload PDF (5036K) -
Shouichi Ochiai1995 Volume 42 Issue 11 Pages 1223-1230
Published: November 15, 1995
Released on J-STAGE: May 22, 2009
JOURNAL OPEN ACCESSAmong various intermetallics, particularly aluminides such as NiAl, TiAl and Nb3Al have received considerable attention as candidates for high temperature materials because of their good properties as high melting temperature, high elevated temperature strength, lower density, superior oxidation resistance. However, poor room temperature ductility and insufficient fabricability at high temperatures, which are inherent in intermetallics, place hurdles on the road to the practical use. Powder metallurgy method is expected to overcome these drawbacks through the refinement of microstructures as well as the near net shaping. Further, by applying mechanical alloying method, it becomes easier to produce intermetallics base composites with both fine and homogeneous structures. This paper provides an outline of my recent investigations on the microstructural and mechanical properties of both aluminides and their composites produced by powder metallurgy method.View full abstractDownload PDF (4267K) -
Kazuo Isonishi, Yasuhiro Naruse, Kenki Hashimoto1995 Volume 42 Issue 11 Pages 1231-1236
Published: November 15, 1995
Released on J-STAGE: May 22, 2009
JOURNAL OPEN ACCESSWe discussed densification behavior of vacuum hot pressing of Nbe25mol%Al composition powder and structural and mechanical property of the compact. Nb-25mol%Al powder was prepared by mechanical alloying for 1800ks and had an average grain size of 7nm. Vacuum hot pressing condition used here was 1173-1273K, 50-200MPa and 10.8ks. Maximum relative density of the compact was 99.8% of theoretical density under the hot pressing condition of 1273K-200MPa-10.8ks. Hot pressed compact consisted of mainly Nb3Al phase and a certain amount of Nb2Al and Nb2C phase. Hot pressed compact exhibited high Vickers hardness value of HV 1520 due to very fine grain size about 30nm and presence of dispersed carbide particle. Creep deformation was occurred over the temperature of 1273K and the compact exhibited value of 5.65 for the stress exponent at 1373K by using high temperature hardness measurement technique.View full abstractDownload PDF (4723K) -
Kazuo Isonishi, Takeshi Kobayashi1995 Volume 42 Issue 11 Pages 1237-1242
Published: November 15, 1995
Released on J-STAGE: May 22, 2009
JOURNAL OPEN ACCESSWe studied mechanical alloying (MA) behavior and phase formation during heating of Nb-75mol%Al powder mixture. Average powder size and particle shape changed discontinuously during MA from flake like particle to fme equiaxed particle. MA Powder had changed to granular shape particle having a diameter about 50μm at 270-360ks milling, 20μm at 540-720ks milling, and less than 5μm over 1440ks milling. This phenomenon was due to the phase change from elemental to intermetallic compounds by milling. From the results of DTA and X-ray diffraction, NbAl3 phase formation occurred after Al melting for short time MAed powder up to 360ks. For longer time MAed powder, having fine lamellar structure, NbAl3 phase was formed at 613-623K. Later exothermic reaction became smaller with increasing MA time because of the formation of NbAl3 phase during MA.View full abstractDownload PDF (5767K) -
Takekazu Nagae, Masateru Nose, Masaru Yokota, Yoshiharu Doi1995 Volume 42 Issue 11 Pages 1243-1246
Published: November 15, 1995
Released on J-STAGE: December 04, 2009
JOURNAL OPEN ACCESSNb-Al intermetallic compounds have been synthesized from Al/Nb or Nb/NbAl3 mixed powders by means of spark plasma sintering (SPS). Hot press sintering (HP) has also adopted to obtain these intermetallic compounds. Results obtained from HP technique were compared with those from SPS technique.
Results obtained were as follows; Nb2Al intermetallic compound was obtained by both process. However, formation of intermetallic compounds was advanced more in SPS than in HP process. Moreover, Nb3Al was synthesized only by SPS process. These differences are thought to come from the effect of pulse electric current of SPS which has originally possessed characteristics SPS process, i.e., activation of powder surface, etc.View full abstractDownload PDF (2727K) -
Keizo Kobayashi, Kazushige Sakazaki1995 Volume 42 Issue 11 Pages 1247-1251
Published: November 15, 1995
Released on J-STAGE: May 22, 2009
JOURNAL OPEN ACCESSFe-5mass%Al was synthesized by mechanical alloying(MA) of Fe powder and Al powder using a vibrational ball milling for 720ks in 35kPa argon gas atmosphere. The MA powder of 6.5nm in grain size was solid solution of Fe and Al in this experimental condition.
Fe-28.6mass%Al(FeAl) sample, which was prepared by mixing of mechanical alloyed t Fe-5mass%Al powder and Al powder, was sintered at 1200K after pressing. The sintered sample was composed of FeAl phase only. As the temperature of reaction between MA powder and Al was higher than the melting point of Al, FeAI was formed under existence of Al liquid. Furthermore, FeAl-40mass%WC composite was synthesized by this process.View full abstractDownload PDF (3964K) -
Nobuyoshi Murakami, Mitsuhiro Hasebe, Kenichiro Shimizu1995 Volume 42 Issue 11 Pages 1252-1257
Published: November 15, 1995
Released on J-STAGE: May 22, 2009
JOURNAL OPEN ACCESSNi-20wt%Al and Ni-30wt%Al powders were prepared from crystalline powders of Ni and Al by the mechanical alloying for relatively short time (108ks). The X-ray diffraction analysis(XRD) showed any compound in as-milled powders. The reaction in heating of these powders was investigated by the differential thermal analysis and the phase formation in powders was observed by XRD and EPMA.
At temperature below eutectic, because the diffusion of Ni in Al grains was prior to that of Al in Ni, Al-solid solution, Al3Ni and Al3Ni2 were formed in order in Al grains, as the temperature increase. At the eutectic temperature, the formation of eutectic melt triggered to nucleate a large number of AJNi3 in Ni grains, followed by the nucleation of AINi. At temperature above eutectic, the stable phase of alloy gradually grew and became predominant as Al continued to diffuse from Al-rich phase to Ni grains. hi a commercial Ni-20wt%Al powder, the reaction in heating was same as that of mechanically alloyed powder, but only a small amount of Al-rich compounds were formed at a low temperature range.View full abstractDownload PDF (3576K) -
Masahiro Inoue, Katsuaki Suganuma1995 Volume 42 Issue 11 Pages 1258-1263
Published: November 15, 1995
Released on J-STAGE: May 22, 2009
JOURNAL OPEN ACCESSNiAl binary and Ni-Fe-Al ternary alloys, with the composition of 40.50at%Al and x ;[Fe]/( [Nil+Fe])=0-0.20, were fabricated by the reactive hot-press sintering. The addition of Fe to NiAl resulted in the decrease of fracture toughness in the case of 50at%AI, however, toughness of 40 and 45at%Al alloys increased to about 30% of the value of NiAl.
NiAl and Ni-Fe-45at%Al matrix composites were fabricated successfully. When the proportionality limit of matrices were <500MPa, it increased by the addition of A12O3 short fibers. In the Ni-Fe-45at%Al matrix composites reinforced by β-SiC whisker, the proportionality limit markedly increased with the addition of under 5vol%. The Al2O3 short fiber and the β-SiC whisker reinforced Ni-Fe-45at%Al matrix composites had higher strength at room temperature than the NiAl matrix ones.View full abstractDownload PDF (2976K) -
Atsushi Hibino1995 Volume 42 Issue 11 Pages 1264-1269
Published: November 15, 1995
Released on J-STAGE: May 22, 2009
JOURNAL OPEN ACCESSCombustion synthesis process has been taken an interest in synthesizing technology of intermetallic compound such as Ni3Al. However, the synthesized compound tend to be porous, and the synthesis process has not been used practically. To realize the process, a method of synthesizing the dense products should be developed. In this paper, preparation of full dense Ni3Al by pressure less combustion synthesis process was investigated.
Some kinds of Ni and Al powders which had different particle sizes were used as initial substances. Ni/Al premixed compacts (Ni:Al=3:1) were made by combinations of the powders. The green compacts were heated in a vacuum furnace, and burned by thermal explosion reaction.
It was found that the dense product was obtained in case of the compact consisted of fine powders. However, a little pore was observed in the product. Accordingly, degassing treatment was introduced during the process, then the nearly full dense product was synthesized. By X-ray and EDX analysis, it was confirmed that the synthesized product became to homogeneous Ni3Al. Therefore, the combustion synthesis process is effective to compose the Ni3Al intermetallic compound.View full abstractDownload PDF (6325K) -
Atsushi Hibino, Manabu Kiuchi1995 Volume 42 Issue 11 Pages 1270-1276
Published: November 15, 1995
Released on J-STAGE: May 22, 2009
JOURNAL OPEN ACCESSTo realize combustion synthesis process of intermetallic compound, a method of synthesizing the dense products should be developed. In my previous paper, synthesis of full dense Ni3Al has been investigated. Consequently, the dense Ni3Al was synthesized in case of using fine powders as initial substances. Incidentally, it is known that Ni3Al intermetallic compound is brittle and that additive of B is effective for improvement of its ductility. In this paper, preparation of full dense B added Ni3Al by pressure less combustion synthesis process was investigated. Fine Ni, Al and B powders were mixed (Ni:Al=3:1 in atomic ratio, B=0.05-1.0mass%), and pressed into cylindrical compacts. The compacts were burned by thermal explosion reaction in a vacuum furnace. However, B added compacts fused during the synthesis. The meltdown might be due to over formation of liquid phase caused by B additive. Accordingly, the mixing ratio of Ni and Al powders was controlled, and then the nearly full dense B added Ni3Al was synthesized. By compressive strength test of the products, it was confirmed that the B added products exhibited ductility. Therefore, the combustion synthesis process is effective to compose Ni3Al intermetallic compound.View full abstractDownload PDF (7113K) -
Nobuhiro Nakabo, Kei Ohsawa, Mistuya Hashii, Kei Ameyama1995 Volume 42 Issue 11 Pages 1277-1282
Published: November 15, 1995
Released on J-STAGE: May 22, 2009
JOURNAL OPEN ACCESSThe microstructure of mechanically ground (MG) Ti-41 mol%Al alloy powder made by a vibratory ball mill, in the as-milled state as well as after heat treatment or vacuum hot pressing, was investigated. A new method for preparing TEM samples was employed which resolved the microstructure of the MG powder, whose particle sizes were more than 10μm in diameter. The alloy powder milled for 720ks was composed of fine grained α2 (Ti3Al), nanocrystals of Al supersaturated α-Ti and an amorphous phase. The a nanocrystals and the amorphpos phase presumably caused by milling of α2 and γ phases, respectively. The vacuum hot pressed compact showed ultra-fine equiaxed grain structure, with an average grain size of approximately 400nm. The similarity of the microstructure to that of mechanically alloyed (MA) compacts strongly suggests that the formation mechanism of the ultra-fine grain structure of the compacts is the same in both MG and MA processes.View full abstractDownload PDF (4270K) -
Akihiro Matsumoto, Kunisuke Andoh, Kiyotaka Katoh1995 Volume 42 Issue 11 Pages 1283-1288
Published: November 15, 1995
Released on J-STAGE: May 22, 2009
JOURNAL OPEN ACCESSRuAl is potentially one of the structural intermetallics with high melting temperature(2333K). We applied mechanical alloying to prepare the intermetallic compounds NiAl and RuAl, which crystal structure are B2 type, using a mixture of elemental Ni, Ru and Al powders. Single phase NiAl have been obtained by ball milling for 75h, while RuAl for 200h. The grain size of NiAl thus obtained was 8.5nm, while RuAl 7nm, that was estimated by the Hall plot. RuAl powder, obtained by mechanical alloying for 400h, was consolidated by Plasma Activated Sintering (PAS) process under the conditions of 50MPa, 1673K and 480sec. Vickers hardness was examined between room temperature and 1373K. RuAl compact obtained by PAS had about two times as high hardness as arc melted RuAl over the whole temperature range measured. Vickers hardness of RuAl compact measured at room temperature was 690Hv and there was no crack around the indentation. The result suggests that RuAl compact had reasonable toughness at room temperature.View full abstractDownload PDF (7145K) -
Hiroshi Mabuchi, Noboru Kiji, Hiroshi Tsuda, Yutaka Nakayama1995 Volume 42 Issue 11 Pages 1289-1294
Published: November 15, 1995
Released on J-STAGE: May 22, 2009
JOURNAL OPEN ACCESSTo enhance the negligible low-temperature ductility and low high-temperature strength of titanium aluminides, TiAl-Ti2AlC composites were made by the combustion reaction process, following arc-melting. The alloy compositions included Ti52Al43C5, Ti50Al45C5 and Ti48Al47C5 in at%. The resulting composites had about l8vol%Ti2AlC in the matrix TiAl with a lamellar structure of Ti3Al. In the annealed specimens, smaller particles were visible in the matrix, and appeared to form in place of solutionizing lamellae. Therefore, carbon atoms in the matrix, probably in the Ti3Al phase, formed carbide Ti2AlC particles with the smaller sizes. On the other hand, the behavior with regard to change in lattice parameters and Vickers hardness suggested a reduction in the solubility of carbon in the TiAl phase with decrease in annealing temperature. For the Ti50Al45C5 alloy, annealed at 1273K, ambient-temperature ductility up to 0.9% was achieved in bending.View full abstractDownload PDF (3991K) -
Junichi Hojo, Yasunori Ishizaka, Kazushi Kishi, Seiki Umebayashi1995 Volume 42 Issue 11 Pages 1295-1299
Published: November 15, 1995
Released on J-STAGE: May 22, 2009
JOURNAL OPEN ACCESSFine MoSi2 powder and MoSi2-10wt%SiC composite powder (particle size: ca. 1μm) prepared by a carbothermal reduction process were hot-pressed at 1600-1900°C to investigate the microstructure and mechanical properties of the sintered bodies. The sintered density of synthesized MoSi2 powder reached 97% of theoretical at 1700°C but decreased at a higher temperature. MoSiZ SiC composite powder re-quired a high temperature of 1800°C for densification. Commercial MoSi2 powder (particle size: 6-12μm) was densified to 99% at a low temperature of 1600°C. The low sinterabilities of the synthesized powders were caused by the formation of closed pores with grain growth. Although the sintered bodies of the commercial powder had the high density, the hardness and fracture toughness were low. On the other hand, the sintered bodies of the synthesized powders had high hardness and fracture toughness owing to the fine microstructures. The hardness and fracture toughness were further improved by SiC inclusions.View full abstractDownload PDF (5630K) -
Mikio Ito, Kazuhiko Majima, Shigeru Katsuyama, Hiroshi Nagai1995 Volume 42 Issue 11 Pages 1300-1304
Published: November 15, 1995
Released on J-STAGE: December 04, 2009
JOURNAL OPEN ACCESSThe preparation of Sm2Fe17Nx magnetic powders by mechanical grinding (MG) in NH3 and subsequent nitrogenation heat treatment without crystallization was carried out. A vibration ball mill with high mechanical energy and a rotary ball mill with low mechanical energy were employed for MG. The effects of ununiform distortion introduced by MG into the powders on their magnetic properties were investigated.
Using a vibration ball mill, the powders after MG and subsequent nitrogenation had very poor rectangularity on their demagnetization curves. Using a rotary ball mill in order to decrease the effects of strain, the powders after MG for 288ks-324ks absorbed sufficient nitrogen of about 35000ppm. In spite of sufficient nitrogen content, their magnetic properties were far from those of hard magnetic materials. The powder with less strain was prepared by MG for 36ks and subsequent nitrogenation. This powder showed good rectangularity on the demagnetization curve, that is, high remanence of about 1 Wb⋅m-2 and high maximum energy product of about 129 kJ⋅m-3. These values are much better than those of powders prepared with a vibration ball mill. Magnetic properties are very sensitive to the distortion introduced by MG. Therefore decreasing distortion of powders is essential to obtain excellent properties as a hard magnetic material.View full abstractDownload PDF (299K) -
Krishnamurthy Raviprasad, Satoru Kakoo, Ken Makita, Minoru Umemoto1995 Volume 42 Issue 11 Pages 1305-1310
Published: November 15, 1995
Released on J-STAGE: May 22, 2009
JOURNAL OPEN ACCESSThe usefulness of a permanent magnet depends on its energy product (BH)max and it is desirable to increase both the coercivity and remanence. Mechanical alloying with its inherent advantage of grain refinement is expected to result in enhanced coercivity. The advantage of grain size refinement by mechanical alloying is fully utilized, if this can lead to remanence enhancement at the same time. Such a thing is possible if nano scale mixture of exchange coupled hard and soft phases are produced. A magnet with such a two phase mixture is called exchange spring magnet. In the present study exchange spring magnets of α-Fe-Nd(Fe, TM)12Nx (where TM=V, Mo) are synthesized by mechanical alloying and a two stage heat treatment. The effect of nitrogenation condition on the magnetic properties has been studied. The optimum nitrogenation temperature was found to be 673 K. Exchange spring magnet of a-Fe-Nd(Fe, Mo)12Nx showed a maximum energy product of 48 kJ/m3 and a spring back of 50%.View full abstractDownload PDF (344K) -
Sunao Sugihara, Shigeru Tomita, Kouji Asakawa1995 Volume 42 Issue 11 Pages 1311-1317
Published: November 15, 1995
Released on J-STAGE: July 12, 2010
JOURNAL OPEN ACCESSThe effects of fabrication process parameters of P-Bi2Te3 on the thermoelectric properties has been studied. The factors are reduction of the powder from the ingot, cold isostatic press and sintering atmospheres of Ar and Ar/7%H2. The size of pow-der less than 355μm was used. As one of results, the lowest electrical resistivity were obtained in the process of using a reduced powder and sintering in the atmosphere of Ar/7%H2, which value at 57°C was 0.8×10-4Ω⋅m as compared to 1.1×10-4Ω⋅m sintered in the Ar atmosphere. Secondly, the results suggested that the tex-ture in the microstructure was important rather than density itself. The Seebeck coefficients of the specimens at 57°C sintered in Ar/7%H2 using a reduced powder showed almost same value of 240μ⋅V/K as the normal powder specimens sinterd in Ar atmosphere. It is concluded that a reducing process positively is not necessarily effective for improving the thermoelectrical properties.View full abstractDownload PDF (3912K) -
Shinya Shiga, Minoru Umemoto1995 Volume 42 Issue 11 Pages 1318-1322
Published: November 15, 1995
Released on J-STAGE: May 22, 2009
JOURNAL OPEN ACCESSIt is necessary to improve the thermoelectric property of many thermoelectric materials. The reduction in thermal conductivity (K) and specific resistance (ρ) is effective to improve the effective maximum power (Peff). In this paper, possibility of the improvement in Peff by the addition of good electrical conductor (Ag) to thermoelectric semiconductor (β-FeSi2) was studied as well as the effect of sample length on Peff. Peff has the optimum sample length (Lmax) which makes the Peff maximum. Lmax is estimated by 2K/C, here C is thermal transfer coefficient. When the temperatures of hot and cold end of sample are fixed, Peff of pure Ag is larger than that of β- FeSi2. But, this condition is not realistic, because temperature difference between hot and cold end of sample (ΔT) depends on K, C and L. On the other hand, when the temperatures of heat source and heat sink are fixed, improvement of Peff by addition of Ag is not obtained for parallel and series composite models. Calculations show that the expected improvement of Peff is not observed by the simple addition of good electrical conductor to thermoelectric semiconductor.View full abstractDownload PDF (291K) -
Hiroshi Nagai, Shogo Nakayama, Hideaki Kobayashi, Shigeru Katsuyama, K ...1995 Volume 42 Issue 11 Pages 1323-1327
Published: November 15, 1995
Released on J-STAGE: July 12, 2010
JOURNAL OPEN ACCESSThe thermoelectric properties of n-type FelyCoySi2Cux(0.02≤y≤0.06)(0≤X≤0.06) and ptype Fe0.92Mn0.08Si2-xCux(0≤X≤0.07) were investigated. Mixture of Fe, Si and Co or Mn powders with or without Cu was arc-melted in an argon atmosphere to form a button composed of α -Fe2Si5 and ε-FeSi phases. The button was ground under -60mesh and Cu powder was mixed for the samples without Cu doping. Then they were ground (MA) in a conventional ball mill for 360 ks or in a high energy vibrational mill for 72 ks. β-FeSi2 phase was not formed during MA, but was obtained by hot pressing of MA powders at 1173 K for 1.8 ks under 25MPa. It was found that the small addition of Cu improves the power factor(Q2/ρ) of n-type Fe1-yCoySi2 by decreasing the electrical resistivity and increasing the thermoelectric power. On the other hand, for p-type Fe0.92Mn0.08Si2 the electrical resistivity slightly increased and thermoelectric power decreased, as the result the power factor decreased. Cu addition slightly increased the thermal conductivity for both of n-type and p-type β-FeSi2.View full abstractDownload PDF (269K) -
Hiroshi Nagai, Takashi Tahara, Shigeru Katsuyama, Kazuhiko Majima1995 Volume 42 Issue 11 Pages 1328-1332
Published: November 15, 1995
Released on J-STAGE: December 04, 2009
JOURNAL OPEN ACCESSThe effect of Al addition on the thermoelectric properties of n-type Fe0.98CO0.02Si2 were investigated for Fe0.98Co0.02Si2-xAlx (0≤ X ≤0.1) and Fe0.98Co0.02Si2 + ywt%Al (0 ≤ y ≤ 6). Mixture of Fe, Si and Co powders with or without Al were arc-melted in an argon atmosphere to form a button composed of α -Fe2Si5 and ε-FeSi phases. The button was ground under -60mesh and Al powder was mixed for Fe0.98Co0.02Si2 powder. Then they were ground (MA) in a conventional ball mill for 360 ks. β-FeSi2 phase was not formed during MA, but was obtained by hot pressing of MA powders at 1173 K for 1.8 ks under 25MPa. It was found that the thermoelectric properties of Fe0.98Co0.02Si2 was drastically changed by the ddition of Al. The resistivity of Fe0.98Co0.02Si2 increased with increasing Al addition and reached at maximum at x=0.04 and y=1, respectively and thereafter decreased again for higher Al content. Thermoelectric power decreased with increasing Al addition and the property drastically changed from n-type(x ≤ 0.04), (y ≤ 1) to p-type(x ≥ 0.06), (y ≥2). As a result, the power factor(Q2/ρ) of Fe0.98Co0.02Si2 decreased with increasing Al addition. On the other hand, the thermal conductivity of Fe0.98Co0.02Si2 slightly increased with increasing Al addition due to the increase in the heat capacity.View full abstractDownload PDF (270K) -
Shigeru Katsuyama, Yoshiyuki Tanaka, Yoichi Shichijo, Kazuhiko Majima, ...1995 Volume 42 Issue 11 Pages 1333-1337
Published: November 15, 1995
Released on J-STAGE: May 22, 2009
JOURNAL OPEN ACCESSThe effect of substitution for La by Ba or Ca on the thermoelectric properties of rare earth chalcogenide La3S4 was examined. Cubic 7 -phase (Th3P4-type) was obtained in the range of 0 ≤y≤1 in La3-yBayS4 and La3-yCayS4. With an increase of y, the lattice parameter in La3-yBayS4 increases, while that in La3-yCayS4 decreases. The electrical resistivity (r) and thermoelectric power (α) of La3-yBayS4 and La3-yCayS4 increase with an increase of y. The maximum power factor α2/r was obtained in La2.8Ca0.2S4 at 500°C. It seems that there is the most suitable value of y for the power factor.View full abstractDownload PDF (259K) -
Hisashi Suzuki, Osamu Terada, Hiroyuki Ike1995 Volume 42 Issue 11 Pages 1341-1344
Published: November 15, 1995
Released on J-STAGE: May 22, 2009
JOURNAL OPEN ACCESSIt has been known by the present authors that mechanical properties of WC-Ni alloy were improved towards the values of WC-Co alloy with decreasing grain size of WC, and also the micro-grained WC-Ni alloy could be obtained by the addition of VC, etc., with the result that small pores were apt to appear in the micro-grained WC-Ni alloy in the sintered state, differing from the case of micro-grained WC-Co alloy. Then, the study on this subject, that is, on the reason why small pores often appear in the micro-grained WC-Ni alloy was carried out. The WC-10mass%Ni alloy containing VC up to 5 mass% in binder was used as specimens.
It was suggested that the fact that the Ni rich agglomerates peculiar to WC-Ni alloy (consisting of Ni and fine WC particles) formed during ball-milling of mixture could not perfectly be removed from the ball-milled mixture, and the fact that the temperature at which liquid phase appeared was higher in WC-Ni alloy by about 701C, comparing with in WC-Co alloy, were the most responsible for the above subject.View full abstractDownload PDF (4108K) -
Hisashi Suzuki, Osamu Terada, Hiroyuki Ike1995 Volume 42 Issue 11 Pages 1345-1349
Published: November 15, 1995
Released on J-STAGE: July 12, 2010
JOURNAL OPEN ACCESSThe micro-grained WC-10mass%Ni medium carbon alloys having additional VC up to 10mass% in binder were sintered in vacuum at 1450-1500°C, using starting WC powder with particle size of 0.7 and 1.4μm. The mechanical properties of the alloys such as hardness(HV) and transverse-rupture strength(σm) were mainly studied as a function of carbide grain size (dWC) in the range from 1.5 to 0.4μm. The results obtained were compared with those of micro-grained WC-10mass%Co alloys previously reported by the present authors.
It was found that the RV and σm of WC-Ni alloy increased with decreasing dWC towards the values of micro-grained WC-Co alloy. It was also found that the above values became almost the same as those of WC-Co alloy, when dWC decreased to the values less than 0.5-0.6μm. The phenomena were in detail discussed from a viewpoint of characteristics different between Ni and Co binder metals.View full abstractDownload PDF (3314K) -
Tatsuro Isomoto, Hiroshi Nagai1995 Volume 42 Issue 11 Pages 1350-1355
Published: November 15, 1995
Released on J-STAGE: May 22, 2009
JOURNAL OPEN ACCESSPowder metallurgy (PM) SUS304 stainless steels consolidated by hot extrusion process with different oxygen contents from about 100 to 250 ppm were investigated in terms of creep properties at elevated temperatures with a comparison of the cast and wrought (CW) material. PM materials show the same level of creep rupture strength as CW material at 650°C, but lower values with increasing temperature to 950°C. This lower creep rupture strength of PM materials is partly due to fine grains resulting from the suppression of grain growth by the dispersion of oxides originated from powder surfaces. With increasing oxygen content, the creep rupture strength and ductility of PM materials are decreased by cavity formation promoted by oxides situated at the grain boundaries.View full abstractDownload PDF (6135K)
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