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Volume 48, Issue 7
Displaying 1-14 of 14 articles from this issue
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Wei Fang, Sung-Yul Lee, Il-Dong Choi, Se-Hyun Ko, Yong-Ho Park2001 Volume 48 Issue 7 Pages 589-593
Published: July 15, 2001
Released on J-STAGE: May 22, 2009
JOURNAL FREE ACCESSPowder compacts for Ti3Al, Ti3Al-7Nb and Ti3Al-13Nb alloys were manufactured by mechanical alloying-pulse discharge sintering at 1273 K and, their microstructure, oxidation resistance and mechanical properties were evaluated. The mechanically alloyed Ti3Al with different Nb contents possessed similar X-ray diffraction profiles, corresponding to alpha titanium. The Ti3Al-Nb powders were sintered for a short time of 600 s at 1273 K, and a complete transformation from the supersaturated alpha titanium structure to Ti3Al were confirmed. The sintered compacts had a homogeneous fine microstructure. Microhardness obviously increased with Nb contents for Ti3AI. Adding Nb clearly improved oxidation resistance of Ti3Al, although the effect decreased at 1273 K.View full abstractDownload PDF (6006K) -
Mitsuru Nakamura, Takashi Umemura, Takeshi Ohba, Yoshimi Sugaya, Chang ...2001 Volume 48 Issue 7 Pages 594-599
Published: July 15, 2001
Released on J-STAGE: May 22, 2009
JOURNAL FREE ACCESSRapid sintering within a few minutes is investigated under nitrogen-hydrogen gas atmosphere. Specimens were composited 0.8mass%C-1.5mass%Cu-bal. Fe powders and rapid sintering was carried out in the high frequency induction heating instrument. In the case added low H2 gas concentration from 1 to 2%, the radial crushing strength and the prevention of decarburization were almost same values compared to rapid sintering of 100% N2 gas atmmsphere. But, when increasing H2 gas concentration, it occurred to lower the radial crushing strength largely. As a result, this lowering tendency of radial crushing strength was caused to form FeOOH compound by the present of H2 gas and this compound prevented to diffusion of Cu elements.View full abstractDownload PDF (3958K) -
Guofeng Zhang, Masao Morishita, Koichiro Koyama2001 Volume 48 Issue 7 Pages 600-606
Published: July 15, 2001
Released on J-STAGE: May 22, 2009
JOURNAL FREE ACCESSThe effects of addition of Cu, Cr and W on the wear resistance and bending strength of the Ni-M3B2 (M=Ni, Cr, Mo, W) two phase alloy were investigated. The wear resistance and bending strength of the alloy were improved by the addition of Cu, Cr and W. The optimum alloy composition was found to be Ni-3.6mass%B-29.3mass%Mo-15mass%Cr-2mass%Cu-18.7mass%W. The wear resistance of the alloy with the optimum composition was superior to the conventional Ni-based wear resistant alloy with the composition of Ni 3mass%B-13.5mass%Cr-4.8mass%Fe-0.8mass%aC. Also, the bending strength of the present alloy showed 1.81 GPa. Furthermore, the corrosion resistance of the present alloy in 6% HNO3 aqueous solution and 10% HCI aqueous solution, was 70 times and 7 times higher respectively, than that of the conventional Ni-based wear resistant alloy. Therefore, the present alloy is expected to be a new corrosion and wear resistant alloy.View full abstractDownload PDF (4420K) -
[in Japanese]2001 Volume 48 Issue 7 Pages 608
Published: July 15, 2001
Released on J-STAGE: May 22, 2009
JOURNAL FREE ACCESSDownload PDF (99K) -
Shuichi Imasato, Shigeya Sakaguchi, Taikou Okada, Yasunori Hayashi2001 Volume 48 Issue 7 Pages 609-615
Published: July 15, 2001
Released on J-STAGE: May 22, 2009
JOURNAL FREE ACCESSIt is well known that the mechanical properties of cemented carbide largely depend on the WC grain size and carbon content. But the influence of WC grain size on the corrosion resistance has not been much studied. In this report, the effect of WC grain size on the corrosion properties of WC-15mass%Co cemented carbides was investigated in 3%NaCl neutral and 3%NaCl+0.1N H2SO4 acidic solutions by the immersion test and the polarization test. In the immersion test, the main dissolved element was Co, and the amount of dissolved Co in 3%NaCl+0.1N H2SO4 was several times lager than in 3%NaCl solution. The amount of dissolved metals in neutral and acidic solution decreased with the decreasing of WC grain size and the carbon content.
In the polarization test, the anodic reaction was the dissolution of the binder metals in both solutions, and the corrosion rate of the WC-Co alloy with smaller WC grain size was lower than that of the alloy with coarse WC grain size. WC-Co alloy with the smaller WC grain size showed a higher corrosion resistance because of the low current densities of active dissolution and passivated region in polarization curve.View full abstractDownload PDF (5823K) -
Minoru Fukunaga, Masahiro Machida, Keizo Kobayashi, Kimihiro Ozaki2001 Volume 48 Issue 7 Pages 616-620
Published: July 15, 2001
Released on J-STAGE: May 22, 2009
JOURNAL FREE ACCESSThe microstructure and mechanical properties of WC-10mass%(Fe-25at%Al), WC-10mass%(Fe-22.5at%Al-5at%B) and WC-20mass%(Fe-25at%Al) alloys were investigated. Fe-25at%Al and Fe-22.5at%Al-5at%B were synthesized by mechanical alloying (MA) for 540 ks of Fe and Al powders, and Fe, Al and B powders, respectively. The obtained MA powders and WC powder were mixed under the wet condition or the dry condition. For the mixing under the wet condition, the attrition ball milling with the organic solvent was used. For the mixing under the dry condition, the planetary ball milling in Ar gas atmosphere was used. The mixtures were consolidated by a pulsed current sintering (PCS) process.
The density and hardness of WC-10mass%(Fe-22.5at%Al-5at%B) alloy prepared by the wet mixing were higher than these of WC-10mass%(Fe-25at%Al) alloy. However, these alloys showed low traverse-rupture strength (TRS) value of 1 GPa because of high oxygen content. WC-10mass%(Fe-25at%Al) alloy prepared by the dry mixing became more homogeneous and higher density with increasing the mixing time. The hardness of WC-10mass%(Fe-25at%Al) mixed for 72ks was more than 93 HRA. WC-20mass%(Fe-25at%Al) alloy prepared by the dry mixing showed almost theoretical density, and thus showed hardness of 90.5 HRA and TRS of 1.3 GPa.View full abstractDownload PDF (7436K) -
Kozo Kitamura, Masaki Kobayashi, Koji Hayashi2001 Volume 48 Issue 7 Pages 621-628
Published: July 15, 2001
Released on J-STAGE: May 22, 2009
JOURNAL FREE ACCESSWe had already reported that WC-Co base hardmetal (W+Graphite+Co alloy) prepared from W+Graphite mixed powder instead of conventional WC powder has a large amount of highly oriented plate-like triangular prismatic WC crystal grains, and that both fracture toughness and transverse-rupture strength are higher than those of the conventional hardmetals at an identical hardness. In this study, we prepared another new WC-Co base hardmetal by using Co, W, C, complex carbide such as CO3W9C4 (K) and Co2W4C (θ) as the main starting material. It was clarified that WC crystal grains in the new hardmetal are also plate-like triangular prismatic, but are not oriented, differing from W+Graphite+Co alloy. The fracture toughness, however, was higher by 10-15% than that of the conventional alloy at an identical hardness, while the transverse-rupture strength was comparable with that of the conventional alloy.View full abstractDownload PDF (6213K) -
Kazuhiko Tanaka, Koji Hayashi2001 Volume 48 Issue 7 Pages 629-635
Published: July 15, 2001
Released on J-STAGE: May 22, 2009
JOURNAL FREE ACCESSPowders of new mono-carbonitride of W, MO and W-70at%Mo alloy, i.e., W(C, N), Mo(C, N) and (W0.3Mo0.7) (C, N) have already been found by the authors to be synthesized by heating the metal and alloy powders at 1373-1573 K in CH4+NH3 mixed gas of normal-pressure. In this study, the effect of some intermediate phases such as Me2C and Me2N (Me: W, Mo and W-70at%Mo), which are generated during the temperature-raising stage, i.e., preheating, on the amount and N content of the mono-carbonitrides, were investigated.
The following were clarified or strongly suggested. (1) W(C, N) is generated from W and W2N, while not from WC. (2) Mo(C, N) is generated from Mo2C and Mo2N, while hardly from Mo. (3) (W0.3MO0.7)(C, N) is generated from all of W-70at%Mo, (W0.3MO0.7)2C and (W0.3MO0.7)2N, while not from (W0.3MO0.7)C. (4) Me2N is an appropriate precursor for these three kinds of mono-carbonitrides, compared with Me, Me2C and MeC. (5) By changing the atmosphere in the temperature-ranging stage from CH4+NH3 to NH3, the nitrogen contents (N/metal) of W(C, N) and Mo(C, N) could be increased from 5 and 17 at% (by the conventional profile) to 9 and 22 at%, respectively, while the nitrogen content of (W0.3MO0.7) (C, N) could not be increased (23 at%).View full abstractDownload PDF (560K) -
Yutaka Yanaba, Koji Hayashi2001 Volume 48 Issue 7 Pages 636-642
Published: July 15, 2001
Released on J-STAGE: May 22, 2009
JOURNAL FREE ACCESSWe have proposed two new estimation methods for the fracture toughness (KIC) of hard or brittle materials by each use of our newly derived two equations of σm=ψKICSmf1/2 and σd-1=σ0-1+Ka1/2 (σm: transverse-rupture strength of artificially un-notched test piece, ψ: shape factor, Smf: total macroscopic fracture surface area of one test piece, σd: maximum external fracture stress which operated on the fracture origin, σ0: intrinsic fracture strength, 2a: maximum fracture origin diameter, K: 2σ0-1ρ-1/2, which is nearly proportional to KIC-1, ρ: fracture origin tip radius). And we have clarified that these two equations and two methods are applicable to some hard or brittle materials such as high speed steel, WC-16.4vol%Co hardmetal, Si3N4 ceramics and Mn-Zn ferrite.
In this study, we clarified that the above two equations and two methods are applicable also to another eight kinds of hard or brittle materials such as WC-Co hardmetals, TiC- and Ti(C, N)-base cermets and Al2O3-base ceramics. The Ψ and K values for each material were clarified to be commonly about 14×103 m-3/2 and 0.70KIC-1 respectively, in the same way as for the above previously studied materials. Thus, it was concluded that the KIC of general new hard or brittle materials can be estimated from σm and Smf or σd and 2a by each use of the above two equations or modified equations where these concrete experimental values of Ψ and K were substituted, respectively.View full abstractDownload PDF (549K) -
Effects of Boron Source on the Microstructures and Mechanical Properties of Mo2NiB2 Base Hard AlloysYuji Yamasaki, Mari Yonetsu, Ken-ichi Takagi2001 Volume 48 Issue 7 Pages 643-647
Published: July 15, 2001
Released on J-STAGE: December 04, 2009
JOURNAL FREE ACCESSA Ni-4.5B-46.9Mo-12.5V (mass%) model alloy made from four kinds of boride powders (MoB, Mo2B, NiB and Ni2B) was prepared to study the effects of boron source on the microstructure and mechanical properties. The alloy made from Ni2B powder showed a very fine ideal two phase microstructure with homogeneous distribution of a tetragonal M3B2 (M: Mo, Ni and V)type complex boride in the Ni base binder and hence exhibited excellent transverse rupture strength (TRS) higher than 3 GPa. The strength of the alloy made from the other boride powder exhibited 2.2-2.6 GPa. Carbon base impurities in the boride powders lead to the formation of carbides which caused deterioration of the mechanical property. The carbide formation changed the composition of the tetragonal boride phase and hence the hardness.View full abstractDownload PDF (1803K) -
Yoshiharu Doi, Kenji Matsuki, Shouichi Ochiai2001 Volume 48 Issue 7 Pages 648-654
Published: July 15, 2001
Released on J-STAGE: December 04, 2009
JOURNAL FREE ACCESSNi3AI (γ')-NiAI(β) two-phase nickel aluminides with or without reinforcement of 10vol.% TiC particles (expressed as 10%TiC and 34Al, respectively) can be fabricated by a wet mechanical alloying and vacuum hot pressing process. Recently, we have reported these two-phase nickel aluminides have very fine grain structure and, thus, show a high strain rate superplasticity. In this study, an effect of two types of heat treatment on the microstructure have been investigated in order to improve a mechanical properties at high temperatures. The microstructure control is on concerning of the change from the fine grain structure suitable for superplasticity to a coarse grain structure or a lamella structure for the strengthening at high temperatures after the superplastic deformation.
The heat treatment to obtain a coarse grain structure in the two-phase nickel aluminides was carried out at 1623 K for 43.2ks. The grain coarsening to about 14μm from 1.2μm in 34Al and to about 8μm from 0.9μm in 10%TiC were attained in average grain sizes. The heat treatment to obtain a lamella structure was consisting of oil quenching from 1623 K and tempering at 1073 K or 1273 K. After this heat treatment, the network like precipitation of γ' phase at the prior β-grain boundaries was observed in all intermetallics. A fine lamella structure was only formed in the network of 34Al tempered at 1073 K.
After both heat treatments, the bending strength and defection to fracture in three point bending test above 873 K, and 0.2% flow stress in compression test above 973 K for 34A1 and 10%TiC were improved, compared with fine grained intermetallics. Especially, the formation of ductile networks of γ' phase surrounding brittle β phase was considered to be effective for improving both high temperature strength and ductility. The heat treatment for the coarse grain structure showed more advantage for strengthening at temperatures above 1173K.View full abstractDownload PDF (7682K) -
Eiichi Sentoku, Mituru Kito, Tatuo Nakagawa2001 Volume 48 Issue 7 Pages 655-659
Published: July 15, 2001
Released on J-STAGE: May 22, 2009
JOURNAL FREE ACCESSIn recent years, many machinable ceramics are used in precision instruments and electronic components. The ceramics with higher machinability and processibility are desired for the miniaturization and lightening of the product. The Si3N4/BN ceramics was developed for the purpose of this improvement. The purpose of this study is to clarify the mechanism for the machinability of known machinable ceramics and newly developed Si3N4/BN ceramics by the orthogonal cutting test and micro-fracture test. The cutting mechanism of both ceramics is discussed from viewpoint of the relation between cutting forces, waveform of the AE signal and SEM image of the cutting surface. In the cutting test by a new type of testing machine, the cutting speed was 0.17 m/s and the depth of cut was 0.2 mm. The main results obtained were follows: (1) The generation interval of the undulate acoustic wave of the AE signal for the Si3N4/BN ceramics is shorter than that for the machinable ceramic. In fact, the developed cracks length was smaller in Si3N4/BN ceramics that has the high machinability. (2) Cutting force and fracture energy for the Si3N4/BN ceramics was both lower than that of the machinable ceramics. In fact, the processing was possible by the small force.View full abstractDownload PDF (3181K) -
Masahiro Yokouchi2001 Volume 48 Issue 7 Pages 660-664
Published: July 15, 2001
Released on J-STAGE: July 12, 2010
JOURNAL FREE ACCESSIn the previous study of the B4C/(W, Mo)B2 hard material, the needle shaped crystals of (W, Mo)B2 were found to be formed by reaction between boron of B4C and tungsten or molybdenum. The needle shaped crystals had effect to improve the bending strength and the fracture toughness. However, the carbon particles appeared on the microstructure after sintering, which were supposed to decrease the strength and the toughness. In this study, boron powder was added on the B4C/(W, Mo)B2 hard materials with the aim of inhibitting the decomposition from B4C to carbon. And the effect of boron content on mechanical properties of the hard material was investigated.
The results were summarized as follows:
(1) The decomposition from B4C to carbon was inhibitted by adding boron powder. And the Vickers hardness was increased by adding boron powder.
(2) The bending strength and the fracture toughness were degraded by adding boron powder.View full abstractDownload PDF (1778K) -
Kazuo Hamashima, Kimihiko Sato2001 Volume 48 Issue 7 Pages 665-669
Published: July 15, 2001
Released on J-STAGE: May 22, 2009
JOURNAL FREE ACCESSThe overlay of boride cermet had been fabricated on low carbon steel by plasma transfered arc welding with the composite powders made from MoB, Ni and etc.. The micro-structure consisted of dispersed Mo2NiB2 particles and Ni matrix had been formed successfully by using the semi-sintered powder. However, this boride cermet is not so suitable to overlay alloy, because it is too difficult to control its microstructure of overlay to various sized steel parts.
Improvement in stability of microstructure was achieved by alteration of the compositions. The composite powders made from CrB, Fe and etc. was welded to carbon steel, and the cermet layers of Mo2(Fe, Cr)B2 ceramics and Fe-Cr alloy were obtained as a result. The microstructure is not so sensitive to welding conditions, due to relative slow growth of Mo2(Fe, Cr)B2 ceramics.View full abstractDownload PDF (7006K)
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