Investigation of Vacuum Hot-Press Sintering Temperatures on the Sintered Characteristics of Cr-31.2 mass% Ti Alloys

Abstract

The aim of this work is to nd the optimal sintering parameters of Cr-31.2 mass% Ti alloys and simultaneously investigate the effects of the TiCr 2 Laves phases. In this study, Cr-31.2 mass% Ti alloys are fabricated by vacuum hot-press sintering. Different compositions of submicron titanium (760 nm) powders are added to micron chromium (4.66 μm) powders. The experiments utilize various hot-press sintering temperatures (1250, 1300, 1350 and 1400 C) with the pressure maintained at 20 MPa for 1 h, respectively. The experimental results show the optimal parameters of the hot-press sintered Cr-31.2 mass% Ti alloys to be 1400 C at 20 MPa for 1 h. The relative density reaches 99.96% and the hardness and TRS (transverse rupture strength) reach 81.93 HRA and 475.73 MPa, respectively. In addition, the increase in temperature of the hot-press sintering is effectively decreased the Cr 3 Ti 3 O and slightly enhanced TiCr 2 phases, which will lead to the better mechanical properties. Signi cantly, the optimal hot-press sintered Cr-31.2 mass% Ti alloys possess a dense microstructure, excellent mechanical property and good electrical conductivity value (1.51 × 10 4 S·cm

Effect of process parameters on the microstructure and mechanical properties of vacuum hot-press sintered Co-50 mass% Cr alloys

“…The SPS is defined as follows: The shaped green compact is heated to a temperature that is typically 0.5-0.9 of the melting point. No liquid is present and atomic diffusion in the solid state produces the joining of the particles and reduction of the porosity [13]. Although the porosity variation in SEM images is hard to see differences after various sintering temperatures, the high-temperature hot-press sintering process leads to a grain coarsening phenomenon as shown in Figure 4 (c,d).…”

“…Notably, the black pores seem to decrease as the hot-press sintering temperature increased (1200°C), as shown in Figure 4(b). When the sintering temperature was raised to 1250 and 1300°C, due to solid-phase sintering (SPS) effects [13], only a few internal pores of the hot-press sintered Co-50 mass% Cr specimens remained in the samples. The SPS is defined as follows: The shaped green compact is heated to a temperature that is typically 0.5-0.9 of the melting point.…”

“…In this work, the mean grain size of the Co-50 mass % Cr alloy hot-press sintered specimens was measured using the Linear intercept method [13]. With the increase in the hot-press sintering temperature (1150 → 1200 → 1250 → 1300°C), the mean grain size increased (1.55 ± 0.18 → 2.18 ± 0.19 → 3.19 ± 0.18 → 3.88 ± 0.16 μm), as shown in Figure 5(a).…”

“…On the other hand, since the hot-press sintering temperature did not reach the liquid phase (1397°C) of the Co-Cr alloy, it was not possible for Co-50 mass % Cr alloys to reach a liquid-phase sintering state. According to the sintering theory, under an atmospheric pressure, it is difficult to achieve a high density (> 95%) of the sintered alloys for SPS [13]. It is clear that SPS is the main sintering mechanism for hot-press sintered Co-50 mass% Cr alloys.…”

“…In order to further enhance the sintering density, the sintering step is carried out simultaneously with the application of high temperature and pressure [13]. Hot-press sintering is an effective sintering method in the P/M process.…”