ZhengMing Sun

A new synthesis reaction of Ti3SiC2 through pulse discharge sintering Ti/SiC/TiC powder

Abstract Ti 3 SiC 2 was synthesized by pulse discharge sintering 4Ti/2SiC/TiC mixture powder in a temperature range of 1250–1450 °C. The purity of Ti 3 SiC 2 was improved to 92 vol% at a sintering temperature of 1350 °C. The microstructure in the synthesized samples was controlled to be fine, coarse and duplex grains, depending on the sintering temperature and time.

Fabrication of TiAl alloys by MA-PDS process and the mechanical properties

Abstract Powders of Ti–50Al and Ti–48Al–2Cr alloys were synthesized through mechanical alloying (MA) and were then sintered and concurrently consolidated by using a pulse discharge sintering (PDS) process. The mechanically alloyed Ti–50Al and Ti–48Al–2Cr powders showed similar X-ray diffraction profiles, corresponding to that of the alpha titanium supersaturated with Al. The TiAl alloys were sintered for a short sintering time of 900 s. The microstructures of these two alloys contains equiaxed gamma TiAl with sub-micron grain size and small amount alpha-2 Ti3Al phase. The alloy with chromium addition showed coarser microstructure and superior mechanical properties to that without additives, at the ambient temperature and at elevated temperatures as well. The fracture strength of the as-sintered Ti–50Al and Ti–48Al–2Cr alloys increased with increasing testing temperature up to about 873 K and a decrease followed up.

A new synthesis reaction of Ti3SiC2 from Ti/TiSi2/TiC powder mixtures through pulse discharge sintering (PDS) technique

Abstract Ti/TiSi2/TiC powder mixtures with molar ratios of 1:1:4 (M1) and 1:1:3 (M2) were first employed for the synthesis of Ti3SiC2 through pulse discharge sintering (PDS) technique in a temperature range of 1100–1325 °C. It was found that Ti3SiC2 phase began to form at the temperature above 1200 °C and its purity did not show obvious dependence on the sintering temperature at 1225–1325 °C. The TiC contents in M2 samples is always lower than that of the M1 samples, and the lowest TiC contents in the M1 and M2 samples were calculated to be about 7 wt% and 5 wt% when the sintering was conducted at the temperature near 1300 °C for 15 minutes. The relative density of the M1 samples is always higher than 99% at sintering temperature above 1225 °C, indicating a good densification effect produced by the PDS technique. A solid-liquid reaction mechanism between Ti-Si liquid phase and TiC particles was proposed to explain the rapid formation of Ti3SiC2. Furthermore, it is suggested that Ti/TiSi2/TiC powder can be regarded as a new mixture to fabricate ternary carbide Ti3SiC2.

Deformation and fracture behavior of ternary compound Ti3SiC2 at 25–1300 °C

Abstract The present paper reports the bending deformation and fracture behavior of polycrystalline Ti 3 SiC 2 sample synthesized from 2Ti/2Si/3TiC powder mixture through pulse discharge sintering (PDS) technique at 1300 °C for 15 min. The four-point bending tests were conducted on the Ti 3 SiC 2 specimens in the temperature range of 25–1300 °C. The results showed that the Ti 3 SiC 2 specimens displayed good plasticity at temperature higher than 1200 °C, which is consistent with those synthesized from Ti/SiC/C powder mixture through hot-isostatic pressing (HIP) technique. The fractography observations reveal that the damage and fracture processes of the Ti 3 SiC 2 specimens mainly include the formation of sliding bands, cleavage steps and grain boundary cracking. The present test confirms that the PDS technique can also be used to synthesize Ti 3 SiC 2 products with high purity and good performance.

Electron correlation effects in the MAX phase Cr2AlC from first-principles

With the help of first-principles GGA+U calculations, the origin of the deviation between the experimental and theoretical data for Cr2AlC was revealed. The structural, electrical and elastic properties of Cr2AlC were well described by considering the Cr 3d on-site Coulomb energy. The temperature effect on the bulk moduli of Cr2AlC was also studied within the quasiharmonic Debye model. Based on the present work, we propose that the electron correlation effects in Cr-containing MAX phases cannot be ignored.

Cyclic Fatigue Crack Propagation Behavior of Ti3SiC2 Synthesized by Pulse Discharge Sintering (PDS) Technique

Cyclic fatigue properties of Ti3SiC2 were investigated. When the crack was shorter, it was always arrested due to rapidly increasing crack-tip shielding. Multiple energy dissipative mechanisms including crack deflecting, branching, delamination and grain bridging are responsible for the observed stable crack propagation and high crack growth resistance in this material

Oxidation of Ti3SiC2 at 1000°C in Air

Oxidation of polycrystalline Ti3SiC2 was investigated at 1000°C by XRD and SEM. Results show that a thin SiO2-rich scale forms after short-term oxidation, but it cannot prevent further oxidation effectively. The TiO2 content increased with increasing time and covered the whole surface eventually. For the long-term oxidation, the oxide scales are layered, the outer layer is comprised of pure TiO2, while the inner layer is a mixture of TiO2 and SiO2. The position of the pre-formed SiO2 layer indicates that it can serve as an initial marker for the subsequent oxidation.

On Equilibrium Ga Intergranular Films in Cr2GaC

The presence of equilibrium intergranular films (IGFs) in metallic systems has long been postulated; compelling evidence for this idea, however, is still lacking. Herein differential scanning calorimetry, in the−60°C to 70°C temperature range, on bulk and Cr2GaC powders was carried out. A sharp endothermic trough, roughly 50°C below the melting point of bulk pure Ga, in the powdered samples was taken to be strong evidence for the presence of IGFs in the latter. The troughs for the sintered body were much more diffuse suggesting that in this case, a distribution of grain boundary thicknesses exists. A temperature dependent adsorption energy is postulated to explain the reversible extrusion and resorption of 100 μm thick Ga micro-pillars.

Synthesis and characterization of nanocrystalline diamond thin film on Ti3SiC2

The authors would like to acknowledge that the diamond deposition in this work was conducted in the microwave plasma reactor in the plasma physics laboratory, University of Saskatchewan, which was purchased with Professor Akira Hiroses Canada Foundation for Innovation (CFI) grant.

Synthesis of MAX Phase (Cr,V)2AlC Thin Films

Multiple target magnetron sputtering technique was employed for the deposition of (Cr,V)2AlC thin films, on the substrate of Si wafer at temperatures ranging from ambient to 840 K. The chemical composition and crystal structure of the deposited thin films were analyzed, surfaces as well the cross sections observed. The experimental results demonstrated that the temperature of the substrate does not affect the chemical composition of the deposited thin films. Deposition at room temperature or moderate elevated temperatures was found to result in amorphous films, whereas crystalline MAX phase thin films were obtained at high temperature. The transition of the substrate temperature was found to be around 743 K. The thin films deposited at temperatures below the transition showed the featureless flat surfaces. At high substrate temperatures, crystalline MAX thin films were formed. When deposited at temperatures near the transition, amorphous/nanocrystalline double layer thin films were deposited.