G.C Chen

Bio: G.C Chen is an academic researcher from New York University. The author has an hindex of 1, co-authored 1 publications receiving 6 citations.

The sintering densification, microstructure and mechanical properties of gamma Ti–48Al–2Cr–2Nb alloy with a small addition of copper

Abstract: Titanium aluminide based alloys are difficult to consolidate by pressureless sintering. A systematic study has been made of the effect of small additions of copper on the sintering densification, microstructure and mechanical properties of gamma Ti–48Al–2Cr–2Nb (in at% throughout). The density of the Ti–48Al–2Cr–2Nb alloy sintered at 1375 °C for 120 min increased consistently from 74% theoretical density (TD) without Cu to >98%TD with an addition of up to 2 at%Cu. The enabling effect of a small addition of Cu is due to the formation of a wetting liquid, supported by dilatometry, differential scanning calorimetry (DSC) and Thermal-Calc analyses. Rapid sintering shrinkage occurred around 1251 °C and 1370 °C corresponding to liquid formation. Transmission electron microscopy (TEM) identified the formation of a Cu- and Cr-enriched hexagonal close-packed Ti(Al, Cr, Cu, Nb) phase with a=0.520 A and c=0.803 A. Its presence increased with increasing Cu content. The compressive, tensile and flexure properties of the as-sintered Ti–48Al–2Cr–2Nb–2Cu alloy were assessed. The tensile properties are similar or superior to those of the Ti–48Al–2Cr–2Nb alloy fabricated by metal injection moulding and sintering while the compression strength is about twice that of the as-cast Ti–48Al–2Cr–2Nb.

Microstructure evolution and tensile properties of conventional cast TiAl-based alloy with trace Ni addition

Abstract: The microstructure evolution and tensile properties of Ti-48Al-2Cr-2Nb-0.25Ni alloy fabricated by the induction skull melting (ISM) process were investigated. Results showed that the influence of trace Ni addition on the cast microstructure was slight, while the γ phase fraction increased relatively. After tensile tests at elevated temperature, nanoscale τ3 particles precipitated within the lamellar colony in the gauge area. The τ3 phase exhibited the specific orientation relationship with the α2 and γ phases: ( 22 4 2 ) τ 3 // ( 40 4 1 ) α 2 // ( 113 ) γ and [ 1 1 00 ] τ 3 //[11 2 0] α 2 //[ 1 10]γ . At elevated temperature, the UTS and ef were enhanced evidently by Ni addition than that of Ti-48Al-2Cr-2Nb alloy. Dislocations were pinned by the nanoscale τ3 precipitates during tensile deformation at elevated temperature. The nanoscale τ3 precipitates and increased γ phase fraction induced by Ni alloying could account for the notable tensile properties in the present work. The precipitation behavior and the main strengthening mechanism were analyzed and discussed in detail.

Synthesis of Nanograined Ti-Al-Cr-Nb-X [X = Ni-P-Coated Graphite and Carbon] Intermetallic Matrix Composites by Mechanical Alloying

Abstract: In the present work, TiAl-based intermetallic matrix composite with second phase reinforcement as Ni-P-coated carbon and graphite powders were synthesized by mechanical alloying route. Graphite powder (20–30 µm) and elemental carbon powders (1–5 µm) were coated with Ni-P by the electroless coating technique, which was added to the elemental powder mixtures of Ti-48Al-1%Cr -1%Nb with 1% composition of either of the two. The powder mixtures were subjected to mechanical alloying at 300 rpm up to 250 h using toluene as a process control agent. The samples were collected after 25 h duration and characterized. The formation of TiAl (γ) and Ti3Al (α 2) phases are confirmed by x-ray diffraction. The formations of these phases were found after milling for 75 h in case of graphite addition and 100 h in case of carbon addition in the intermetallic matrix. The mechanically alloyed samples milled for different extents of time were examined by a field emission scanning electron microscope (FESEM) and energy dispersive ...