Key Engineering Materials Vols. 375-376

Abstract: Electroplated Cr, Ni and Cu were used as interlayer for chemical vapor deposition (CVD) diamond coating on WC–Co cemented carbide cutting tools. The electroplated interlayers were studied by Scanning Electron Microscope (SEM), Electron Probe Micro Analyzer (EPMA) and X-ray diffraction (XRD). The CVD diamond coatings were studied by SEM and Raman Scattering Spectroscopy (Raman). The experimental results show that there is diffusion bonded interface between electroplated layer and WC-Co substrate after H plasma treatment, the bond between electroplated layers and WC-Co substrate changes from mechanical bond to metallurgical bond and the adhesion becomes stronger. Electroplated Cr interlayer forms new phases of Cr3C2 and Cr7C3 under CVD conditions, while electroplated Ni and Cu interlayers do not form carbides under CVD conditions. Cr carbides have good chemical compatibility to diamond, and they are propitious to diamond nucleation and growth during the deposition period. The diamond crystal microstructure, diamond quality and adhesion on Cr interlayer are better than those on electroplated Ni and Cu interlayers.

Abstract: In order to investigate the effect of hot-press fabrication parameters on mechanical properties of Al2O3 ceramic tool materials, the orthogonal experiment method was used. In the experiments, the three influence factors such as the fabrication temperature, pressure and duration time are considered. The experimental results are analyzed by a range analysis of orthogonal experiments. It is shown that the most important factor that affects the mechanical properties is the fabrication temperature and the followed factors are the fabrication pressure and the duration time of fabrication. Scanning electron microscope (SEM) reveals that the hot-press fabrication parameters will significantly affect the microstructure of ceramic tool materials, which can govern the mechanical properties. This has been validated by the orthogonal experiments in the present paper.

Abstract: The two cutting tools obtained from ultra-fine grade Ti (C,N)-based cermets were tested in the dry cutting of a medium carbon steel (AISI1045). Microstructure and mechanical properties were studied. Wear mechanisms (mainly diffusion and oxidation) were investigated in detail and compared each other in order to better understand key aspects due to thermal wear mechanisms. Comparing tool A with B, under the adopted cutting conditions, the tool A has a better resistance to oxidation deformation in machining medium carbon steel due to the higher hardness, although tool B has higher bending strength and fracture toughness.

Abstract: This paper studied the axial tensile properties of the multidirectional filament wound tubes (MFWT) both theoretically and experimentally. Based on the Classical Laminate Theory, the mechanical analysis model of the tubes was established and implemented by the program of Matlab language, from which the axial tensile strength was predicted. Then the specimens with different parameters were fabricated and tested under axial tensile load respectively. The theoretical model met the experimental results well. Furthermore, the test results, the stress-strain curve and the failure form were analyzed, which showed that the axial properties of the MFWT were obviously strengthened with the incorporation of the axial reinforcement.

Abstract: The suspension of multi-phase and multi-scale nanocomposite ceramic powders that showed long-term stability was obtained via a series of dispersing technologies including ultrasonic stirring, ball milling and adding dispersant etc. The effectiveness of preventing the suspension from agglomeration by adding the dispersant PMAA-NH4 is better than that of adjusting the pH value of the suspension with aqueous ammonia and hydrochloric acid or adjusting the pH value with aqueous ammonia and hydrochloric acid together with adding PMAA-NH4. A special microstructure was found through TEM that an α-Al2O3 particle is environed by TiN and Ti (C7N3) particles.

Abstract: Basing on the theoretical study on the stress intensity factor (SIF) of the crack parallel to and lying on the interface of the cermet cladding part, the finite element analysis (FEA) of the crack’s SIF is made. The change laws of the SIF with the load action angleψ, the load Q, the clad thickness ratio h1/h and the elastic modulus ratio E1/E2 are obtained. The research results have theoretical and steering significance on the wide application of the cermet cladding part.

Abstract: High residual stress that includes thermal and intrinsic stress is an obstacle to the further application of chemical vapor deposited diamond thick film. In this paper, CVD diamond thick film was deposited on silicon substrate by hot filament chemical vapor deposited (HFCVD) system. The finite element analysis (FEA) simulation and experimental research were carried out on the thermal and intrinsic stress of large area diamond thick film. The FEA model is set up to investigate the distribution and magnitude of thermal stress. The intrinsic stress is studied by X-Ray diffraction “sin2ψ” method. The thermal stress and intrinsic stress are both compression stress. Simulation results show the discontinuous sharp of the diamond film result in the stress concentration and low cooling velocity is a good way to reduce thermal stress. The intrinsic stress is correlative with the microstructure and non-diamond component of diamond film. The origin of the intrinsic stress is discussed in detail in this paper.

Abstract: A series of self-toughening silicon nitride matrix nanocomposite ceramic tool materials are fabricated by hot-press technology at different sintering processes. And their microstructure has been observed and analyzed by a scanning electron microscope (SEM). Finally, the tests of mechanical properties and the cutting performance of the new ceramics are presented. The research results showed that the nanocomposite ceramic tool materials GGW20T5 and GGW20TC25 have better mechanical properties and possess a stronger wear resistance in cutting 40Cr alloy steel.

Abstract: The composition, processing technology, mechanical property and engineering performance of ceramic materials such as cermet, ZTA, TZP, TZP/Al2O3, PSZ, Si3N4 and Sialon, etc, have been predominantly summarized when they are used as die materials in various operations such as drawing, extrusion, punching and stamping etc. The problems existed in the research and application of ceramic die materials are discussed, and the perspectives in the application of ceramic die materials are pointed out. It is concluded that advanced ceramic material is one of the most promising die materials because of its high hardness, high wear resistance, superior high-temperature property and chemical stability and good engineering performance, compared with other die materials such as die steel and cemented carbides. It is proposed that nano composite and functionally gradient ceramic, surface modification technology with ceramic, optimal design of die structures and die reliability research, etc. are all the potential and effective methods in the improvement of mechanical property and engineering performance of ceramic die materials.

Abstract: Diamond thin films doped with various boron concentrations were grown on WC-Co cemented carbide tools by hot-filament-assisted chemical vapor deposition (HFCVD). The trimethyl borate dissolved in acetone solution was used as the boron resource (B/C=0%, 0.1%, 0.3%, 0.5%). The surface morphology of diamond films with different boron contents was investigated by Scanning electron microscopy, the adhesive strength was calculated by means of indentation test under a load of 1500N. A real cutting performance was carried out on Al metal matrix composites material (20vol%SiC, 15μm), and the insert flank wear was examined by measuring the scars that appeared on the cutting edge with tool microscope. The research results shown the surface morphology and structure of the diamond films changed owing to boron doping. As the doping levels increased, the average grain size of the films decreased from 10 to 2μm. A significant improvement in adhesion and cutting performance were observed as the boron contents increased from 0% to 0.5%. The adhesion and cutting performance were best when the boron concentration was 0.3%. Adequate boron can effectively suppress the cobalt diffusion to the substrate surface and avoid the catalytic effect of cobalt at the high temperature. It is of great significance for improvement of the adhesive strength and cutting performance of diamond-coated tools using above method.