Tzu-Piao Tang

Effects of sintering process and heat treatments on microstructures and mechanical properties of VANADIS 4 tool steel added with TiC powders

Abstract In this study, commercial VANADIS 4 (V-4) tool steel powders were classified by sifting, which was previously the matrix, and fine TiC powder was used as an additive to produce a new material with high hardness and wear resistance, via powder metallurgy and a sintering process. Experimental results showed that the transverse rupture strength of the original V-4 steel powder was 678·5 MPa and was enhanced to 868·6 MPa below 25 μm, after the addition of 35 wt-%TiC powders through sintering at 1400°C. In addition, the hardness increased to 86·2 HRA, transverse rupture strength reached 1059·3 MPa and porosity decreased to 1·2% of the V-4 steel powders (below 25 μm) added with 35 wt-%TiC after sintered at 1400°C and annealed at 850°C, followed by quenching at 1030°C and tempering at 200°C.

Enhancement of thermal cracking and mechanical properties of H13 tool steel by shot peening treatment

Abstract Shot peening treatment uses special steel shot media to impact the surface material at a high speed, thus resulting in a compressed and dense surface. The compressive stress provides higher resistance to thermal fatigue and stress corrosion cracking. To evaluate the effects of shot peening on thermal cracking and the mechanical properties of H13 tool steel, this study conducted impact, thermal fatigue and wear tests, as well as SEM microstructure and microhardness inspections. Experimental results showed that steel shot peening treatment, conducted for 30 min at 0·5 MPa on H13 tool steel reached the optimum for improving the microstructure and fatigue properties. The process can enhance the surface hardness to HV 561 and extend the limit of fatigue strength on H13 tool steel by two to three times. This technology can be successfully applied to die casting moulds to notably improve and extend tool life.

Effects of Zinc Oxide and Porosity on Permittivity of Sintered Zinc Sulfide-Silicon Dioxide

The dielectric constants of hot-pressed ZnO-containing 80 at. % ZnS–20 at. % SiO2 dielectric ceramics are analyzed at a frequency range varied from 1 MHz to 1 GHz. Their relative densities are controlled to range from 85 to 99% by varying the hot press pressures. A linear relationship is observed between dielectric permittivity and sintering density. The measured permittivity at 13.56 MHz frequency is found to range from 6.3 to 8.03, which is higher than the estimated values for composite materials using the Bruggeman and Lichtenecker equations. The large grain boundary area arising from nanosized grains contributes to the increase in permittivity. Additions of 0.5–5 wt % zinc oxide then increase the permittivity by forming nanosized Zn2SiO4 willemite phase on the surfaces of SiO2 particles. The presence of ZnO also stabilizes the high-temperature ZnS wurtzite phase to room temperature.