Yunrong Zheng

Fracture Mode of a Ni-Based Single Crystal Superalloy Containing Topologically Close-Packed Phases at Ambient Temperature

The fracture mode of an experimental Ni-based single crystal superalloy containing topologically close-packed phases at ambient temperature was investigated by a simple and practical testing method. Microstructural investigation and compositional analyses were performed on the matching fracture surfaces of a small scale specimen after the impact experiment. It is suggested that the weak TCP/γ′ interface coherency resulted in the interfacial decohesion, which was the main fracture mode for the investigated superalloy under the impact load at ambient temperature.

Solidification microstructure formation in HK40 and HH40 alloys

The microstructure formation processes in HK40 and HH40 alloys were investigated through JmatPro calculations and quenching performed during directional solidification. The phase transition routes of HK40 and HH40 alloys were determined as L → L + γ → L + γ + M7C3 → γ + M7C3 → γ + M7C3 + M23C6→ γ + M23C6 and L → L + δ → L + δ + γ→ L + δ + γ + M23C6 δ + γ + M23C6, respectively. The solidification mode was determined to be the austenitic mode (A mode) in HK40 alloy and the ferritic–austenitic solidification mode (FA mode) in HH40 alloy. In HK40 alloy, eutectic carbides directly precipitate in a liquid and coarsen during cooling. The primary γ dendrites grow at the 60° angle to each other. On the other hand, in HH40 alloy, residual δ forms because of the incomplete transformation from δ to γ. Cr23C6 carbide is produced in solid delta ferrite δ but not directly in liquid HH40 alloy. Because of carbide formation in the solid phase and no rapid growth of the dendrite in a non-preferential direction, HH40 alloy is more resistant to cast defect formation than HK40 alloy.

TRANSIENT LIQUID PHASE BONDING OF SECOND AND THIRD GERNERATION Ni-BASED SINGLE CRYSTAL SUPERALLOY WITH Hf-CONTAININGINTERLAYER ALLOY

A Hf-containing Ni-based alloy was used as the interlayer alloy of TLP bonding for the 2nd (CMSX-4, as-cast condition) and 3rd (SXG3, standard heat treatment condition) generation Ni-based single crystal *国家自然科学基金项目 51071016,国家高技术研究发展计划项目2012AA03A511和教育部技术支撑重点项目625010337资助 收到初稿日期: 2015-07-23,收到修改稿日期: 2015-11-21 作者简介:郁峥嵘,男, 1986年生,博士生 DOI: 10.11900/0412.1961.2015.00408

Effect of Co on Discontinuous Precipitation Transformation with TCP Phase in Ni-based Alloy Containing Re

The effect of Co on discontinuous precipitation (DP) transformation involving the formation of topologically close-packed (TCP) phase was investigated in three Ni-Cr-Re model alloys containing different levels of Co. One typical TCP phase, σ, was generated within DP cellular colonies along the migrating grain boundaries in experimental alloys during aging treatment. As a result of the increased solubility of Re in the γ matrix and enlarged interlamellar spacing of σ precipitates inside of growing DP colonies, Co addition suppressed the formation of σ phase and associated DP colonies. This study suggests that Co could potentially serve as a microstructural stabilizer in Re-containing Ni-base superalloys, which provides an alternative method for the composition optimization of superalloys.

Different Effect of Co on the Formation of Topologically Close-Packed Phases in Ni-Cr-Mo and Ni-Cr-Re Alloys

In current study, two sets of Ni-based alloys (Ni-Cr-Mo and Ni-Cr-Re series) containing 0 to 15 at. pct of Co addition were investigated to understand the formation behavior of TCP phases. Significant difference on the formation behavior of TCP phases and corresponding Co effect was found in two series alloys. TCP precipitates (P and µ phase) were observed in both grain interiors and boundaries in Ni-Cr-Mo series alloys. Higher levels of Co addition increased the supersaturation of Mo in the γ matrix, which explained that Co addition promoted µ phase formation. In contrast, the TCP precipitates (σ phase) formed by the manner of discontinuous precipitation transformation in the grain boundaries in Ni-Cr-Re series alloys. More Co additions suppressed the formation of σ phase, which was mainly attributed to the decreased supersaturation of Re in thermodynamically metastable γ matrix. The information obtained from simplified alloy systems in this study is helpful for the design of multicomponent Ni-based superalloys.