Akio Nishiyama

CVD DIAMOND COATED INSERT FOR MACHINING HIGH SILICON ALUMINUM ALLOYS

Abstract This paper shows the wear mechanism of CVD diamond inserts in machining high silicon aluminum alloys. The tool life of a coated insert with a thin diamond layer is very short due to the easy peeling of the diamond layer. Tool wear of an insert coated with a thick diamond layer is promoted in two steps. In the first step, tool wear occurs continuously by diamond grains chipping and falling off the flank face. In the second step, deep cracks are propagated and reach the surface of the substrate at the threshold of the diamond thickness, remaining due to continuous tool wear, and the diamond layer unexpectedly peels off from the substrate. The flank wear determines the tool life in the machining high silicon aluminum alloys. An improvement in the diamond layer resulting in high resistance to chipping and cracking is required in order to increase the tool life for machining high silicon aluminum alloys.

Effect of grain morphology and grain size on the mechanical properties of Al2O3 ceramics

Bending strength, fracture toughness, fracture energy and crack extension resistance were evaluated for Al2O3 ceramics with equi-axed and platelet grains. Bending strength was proportional to grain size−1/2, but flaws with a size of 10 μm controlled the strength when the microstructure was finer than 10 μm. Fracture toughness, measured by the single etched precracked beam (SERB) method, was proportional to fracture energy1/2, and increased with the grain size of Al2O3 ceramics with equi-axed and platelet grains. However, the toughness of platelet grain ceramics was higher than the ceramics with equi-axed grains, and increased up to 6.6 MPam1/2 with grain size. Therefore, it is thought that fracture toughness not only depends on grain size, but also on grain morphology; equations were derived to account for this phenomenon.

Microstructure and fracture characteristic of Si3N4ZrO2(MgO) ceramic composite studied by transmission electron microscopy

ZrO{sub 2}, which is well known as a phase transformation toughening ceramic, has been widely used as a toughening agent in Si{sub 3}N{sub 4} and Al{sub 2}O{sub 3} matrix composites to improve their mechanical properties. In the Si{sub 3}N{sub 4}-ZrO{sub 2} composites, unstabilized or Y{sub 2}O{sub 3} partially stabilized ZrO{sub 2} is usually used as raw powders, and values of fracture strength and toughness increase with increasing the volume fraction of ZrO{sub 2} up to about 30%, whereas hardness decreases. Therefore, an optimum content of ZrO{sub 2} is desirable for the application of a wear part. Also, ZrO{sub 2} is expected to play the role of a sintering additive. There were many reports on fabrication and mechanical properties for the Si{sub 3}N{sub 4}-ZrO{sub 2} composites, but the relationship between microstructures and a fracture characteristic has little reported until now. In this study, the authors present the results of microstructures and fracture characteristics studied by transmission electron microscopy (TEM), scanning electron microscopy (SEM) and a micro-indentation fracture technique for a Si{sub 3}N{sub 4}-5wt.%ZrO{sub 2}(5wt.%MgO) composite.

Effect of a small amount of liquid-forming additives on the microstructure of Al2O3 ceramics

Sintering behaviour and microstructure of Al2O3 ceramics without additives and with 0.02−0.25 mol% CaO + SiO2 (CaO/SiO2 = 1) were investigated. When Al2O3 bodies were sintered at 1400 °C, the sinterability and the grain size decreased as the content of CaO + Si2 increased. When Al2O3 ceramics with 0.05 − 0.25 mol% CaO + SiO2 were sintered at higher sintering temperature, both CaO and SiO2 reacted with Al2O3 to produce the liquid phase along grain boundaries, and exaggerated platelet Al2O3 grains, with an aspect ratio of about 4.5, were formed. Because the size of platelet grains decreased as the content of CaO + SiO2 increased, the distribution of either SiO2 particles or this intergranular phase of CaO − Al2O3 − SiO2 might control the microstructure.

A study of the adhesion between CVD layers and a cemented carbide substrate by AEM analysis

Abstract The interface between chemical vapor deposition (CVD) coated layers and cemented carbide substrate of coated cemented carbide inserts was analyzed by analytical electron microscopy (AEM). This analysis was carried out from the viewpoint of the adhesion of the coated layer. From the results of elemental analysis, it became clear that the amounts of W and Co diffused from the substrate into the coated layer were different among three coating conditions. A columnar TiCN grain produced in relatively low temperature scarcely contained these elements, and they were detected only at the grain boundary. On the other hand, these elements diffused inside the grains when the shape of the grain was granular as TiN. Strong adhesion of coated layer was obtained when a proper amount of these elements was diffused. Coated inserts containing an interfacial layer with suitable diffused materials and main columnar TiCN layer showed good cutting performance.

CVD Material Processing. Unveiling the Magic of H2S on the CVD-Al2O3 Coating.

CVD-Al2O3層は基体上で均一な層厚の被膜を得にくい等の問題がある. これはCVD反応ガス中に微量のH2Sを添加することで改善されるが, その機構は明らかになっていない. 本研究ではH2Sの添加がCVD-Al2O3反応の均一被覆性向上に及ぼす影響を, 気相に存在する粒子に焦点を当て考察した. 気相中の直径200nm以上の微粒子個数濃度をパーティクルセンサーで計測した結果, H2Sがない場合108/m3以上だった微粒子濃度が, H2S添加量の増加と共に減少し, 0.20%の添加でバックグラウンドレベルの106個/m3以下になった. H2SによるCVD-Al2O3成膜プロセスの改善は, 気相中Al2O3前駆体のサイズダウンによる拡散係数の増大が影響していると考えられる.