Hironori Takahashi

Quantitative determination of the adhesive fracture toughness of CVD diamond to WC–Co cemented carbide

Well-separated diamond particles were nucleated and grown by hot filament chemical vapor deposition HFCVD onto WC)Co cemented carbide pretreated by Murakamis reagent and H O q H SO solution. The adhesive strength of diamond 22 2 4 particles to WC)Co cemented carbide was quantitatively determined in terms of interface toughness by directly applying an external load to the CVD diamond particles. From the measurement of the maximum load required to scratch off the particles, we determined that the adhesive toughness was 14 Jrm 2 . This value is more than twice as high as that of CVD diamond on smooth silicon substrate and comparable to the cleavage fracture energy of diamond. The newly developed procedure will allow to check the effectiveness of substrate surface pretreatments for further improving the adhesion level of diamond films on WC)Co. Q 2000 Elsevier Science S.A. All rights reserved.

Effect of WC-Co substrates pre-treatment and microstructure on the adhesive toughness of CVD diamond

Well separated diamond particles were nucleated and grown by hot filament chemical vapor deposition (HFCVD) onto Co-cemented tungsten carbide (WC-Co). Two carbide grades were prepared. The former one was a ISO grade K10 carbide having a 1-μm average WC grain size, 5.8 wt.% Co and 0.2 wt.% VC. The latter one had a 6-μm average WC grain size, with 6 wt.% Co. Prior to deposition the substrates were submitted to two different pretreatments. The adhesive strength of deposited diamond crystallites was quantitatively determined in terms of interface toughness by directly applying an external load to the CVD diamond particles in the scanning electron microscope (SEM). The adhesive toughness was determined from the measurement of the maximum load required to scratch off the diamond crystallites. The variation of adhesive toughness was correlated to both the microstructure and the pretreatments of the substrate.

Fracture strength of chemically vapor deposited diamond on the substrate and its relation to the crystalline structure

Abstract The mechanical strength of chemically vapor deposited diamond is characterized in terms of fracture toughness. The toughness of film and adhesion interface to the substrate were independently measured using techniques recently developed by the authors. In this paper, diamond was deposited by microwave plasma chemical vapor deposition using a variety of deposition conditions. The fracture toughness of the interface initially increased and then decreased with increasing amounts of methane in the source gas mixture. On the contrary, the toughness of the films was simply found to decrease with respect to the increment of methane concentration. This interesting trend of toughness was explained by the crystalline structure of the deposited diamond.

Fracture toughness of the interface between CVD diamond film and silicon substrate in the relation with methane concentration in the source gas mixture

Diamond films produced by chemical vapor deposition (CVD) have been reported to show various excellent properties. However, low toughness of diamond films, especially the interface between the films and substrates, has been a severe problem. In order to find the dominant factors to control the adhesive strength of CVD diamond films, we obtained diamond films with various crystalline structures deposited on silicon (100) substrates under various methane concentrations in the source gas mixture. The toughness of the interface between the diamond film and silicon substrate was evaluated for the first time by a recently developed method. The toughness showed an interesting behavior with respect to the variation of methane concentration. The obtained results were quantitatively compared to the data already obtained for the case of CVD diamond particles deposited on silicon substrates.

Quantitative comparison of adhesive toughness for various diamond films on Co-cemented tungsten carbide

A new method of quantitative evaluation for the toughness of interface between thick diamond films and Co-cemented tungsten carbide (WC-Co) substrates is reported. This new method derives from the previously developed technique, which was applied for the quantitative evaluation of the adhesive toughness of discrete diamond crystallites on Co-cemented tungsten carbide (WC-Co) substrates [S. Kamiya et al., Diamond Relat. Mater. 9 (2000) 191-194] and has been applied here to evaluate the adhesive toughness of various diamond films on WC-Co cutting inserts. The adhesive toughness was successfully obtained to be in the 15-1.3 J/m(2) range and was depending on the morphology of the interface

A case of idiopathic type 1 diabetes with subsequent recovery of endogenous insulin secretion despite initial diagnosis of fulminant type 1 diabetes

Fulminant type 1 diabetes is characterized by remarkably rapid and complete β-cell destruction. The established diagnostic criteria include the occurrence of diabetic ketosis soon after the onset of hyperglycemic symptoms, elevated plasma glucose with relatively low HbA1c at the first visit, and extremely low C-peptide. Serum C-peptide levels remain extremely low over a prolonged period. A 26-year-old-man with diabetic ketosis was admitted to our hospital. His relatively low HbA1c (7.6%), despite marked hyperglycemia (593 mg/dL) with marked ketosis, indicated abrupt onset. Islet-related autoantibodies were all negative. His data at onset, including extremely low serum C-peptide (0.11 ng/mL), fulfilled the diagnostic criteria for fulminant type 1 diabetes. However, his fasting serum C-peptide levels subsequently showed substantial recovery. While fasting C-peptide stayed below 0.30 ng/mL during the first two months post onset, the levels gradually increased and thereafter fluctuated between 0.60 ng/mL and 0.90 ng/mL until 24 months post onset. By means of multiple daily insulin injection therapy, his glycemic control has been well maintained (HbA1c approximately 6.0%), with relatively small glycemic fluctuations evaluated by continuous glucose monitoring. This clinical course suggests that, despite the abrupt diabetes onset with extremely low C-peptide levels, substantial numbers of β-cells had been spared destruction and their function later showed gradual recovery. Diabetes has come to be considered a much more heterogeneous disease than the present subdivisions suggest. This case does not fit into the existing concepts of either fulminant type 1 or ketosis-prone diabetes, thereby further highlighting the heterogeneity of idiopathic type 1 diabetes.