Yanli Wang

Reaction mechanism in high Nb containing TiAl alloy by elemental powder metallurgy

High Nb containing TiAl alloy was fabricated in argon atmosphere by reactive hot pressing process. Reaction mechanism was investigated by means of microstructural analyses and thermodynamic calculations. The results show that it is feasible to prepare high Nb containing TiAl alloy with fine lamellar colonies by reactive hot pressing process. The reaction between Ti and Al powders is dominant in Ti-Al-Nb system. Nb powders dissolve into the Ti-Al matrix by diffusion. Pore nests are formed in situ after Nb powders diffusion. The hot pressing atmosphere is optimized by thermodynamic calculations. Vacuum or argon protective atmosphere should be adopted.

Diffusion behavior of Nb element in high Nb containing TiAl Alloys by reactive hot pressing

Abstract Diffusion behavior of Nb in elemental powder metallurgy high Nb containing TiAl alloys was investigated. The results show that Nb element dissolves into the matrix by diffusion. Pore nests are formed in situ after Nb diffusion. With the increase in hot pressing temperature, the diffusion of Nb will be more sufficient, and the microstructure is more homogeneous. Nb element diffuses completely at 1400°C. Meanwhile, compression deformation and agglomeration phenomena of pores are observed in some pore nests. Hot isostatic pressing (HIP) treatment can only efficiently decrease but not eliminate porosity completely.

Coarsening and age hardening behaviors of γ′ particles in GH742 during high temperature treatment

The coarsening and ageing hardening behaviors of γ′ particles in superalloy GH742 have been investigated by field emission scanning electron microscopy (FESEM), coarsening kinetics calculation and microhardness testing when ageing at 1050, 950 and 900 °C for different time. The cube of γ′ particle size and ageing time follows a linear law as predicted by LSW theory. The particle size distributions give better fit to the LSW theoretical distribution. The activation energy for γ′ coarsening is accurately determined to have 245. 06±14. 42 kJ/mol when considering the effect of temperature on the solution concentrations in matrix. Based on the activation energy, the coarsening kinetics of γ′ particle is predicted as

Isothermal corrosion Fe3Si alloy in liquid zinc

bar r_t^3 = 7.35 times {10^{15}}frac{{{C_e}}}{T}exp frac{{ - 245,060 pm 14,420}}{{RT}}t

Homogenization treatment of high Nb containing TiAl alloys with as-cast and as-forged microstructures

. The microhardness studies indicate that microhardness decreases rapidly with increasing the ageing temperature and it has a maximum value corresponding to a critical particle size beyond which the microhardness increase stalls with increasing the ageing time.

Densification behavior of high Nb containing TiAl alloys through reactive hot pressing

Abstract The isothermal corrosion testing, microscopic examination and the performance of Fe 3 Si alloy as materials of construction for bath hardware in continuous hot-dipping lines were studied. The corrosion of Fe 3 Si alloy in molten zinc was controlled by attacking the grain boundaries preferentially. Aluminum reacted with iron of Fe 3 Si alloy firstly while the samples were immersed in molten zinc, although aluminum contents in the molten zinc were very low. The phase of reaction product was thought to be Fe 2 Al 5 . The corrosion rate of the Fe 3 Si alloy in molten zinc was determined to be approximately 2.9×10 −3 mm/h, therefore the liquid zinc corrosion resistance of Fe 3 Si alloy was very weak.

Ordered α2 to ωo phase transformations in high Nb-containing TiAl alloys

Abstract The effect of heat treatment on the microstructure evolution of a high Nb containing TiAl alloy has been studied. The results indicate that β-segregation, α-segregation and S-segregation in the as-cast and as-forged alloys can be effectively eliminated at the temperature above T α (1350-1400°C) for long holding time (12-24 h) and the full lamellar (FL) microstructure is gained. For the two alloys, the lamellar colony sizes are 120 μm and 2000 μm, respectively after heat treatment at 1400°C for 12 h. Meanwhile, the sizes are 210 μm and 3000 μm, respectively at 1350°C for 24 h. To get a fine homogenous microstructure, the primary as-cast alloy is first subjected to preheat treatment for eliminating the segregations. After the preheat treatment, the alloy is processed by the multi-step canned forging to attain the microstructure with fine grain size.

Microstructure and mechanical properties of as-cast Ti–45Al–8.5Nb–(W,B,Y) alloy with industrial scale

Abstract Densification behavior of high Nb containing TiAl alloys through reactive hot pressing was investigated. The results showed that the density of the sample hot pressed at 1400°C could reach a near full density of 98.37%. However, the densification abnormality was observed at 1500°C. The diffusion of elemental Nb during microstructural evolution is an important aspect affecting densification, which will form pore nests. With the increase of hot pressing temperature, the diffusion of Nb becomes more adequate. HIP (Hot isostatic pressing) treatment can only decrease porosity to some extent, but cannot eliminate it completely.