Xianfei Ding

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

Development of High Performance Cast Iron with Combination of Improved Mechanical and Thermal Properties Through Mo Addition

High performance cast iron with a combination of improved mechanical properties and thermal conductivity is developed through Mo addition in gray cast iron. The primary austenite dendrite as well as the eutectic cell can be refined by Mo addition. Decrease of the amount and length of graphite flakes as well as Mo solid-solution strengthening leads to high ultimate tensile strength, while the uniform distribution of graphite flakes is responsible for the improved thermal conductivity.

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.

Microstructure evolution in grey cast iron during directional solidification

The solidification characteristics and microstructure evolution in grey cast iron were investigated through Jmat-Pro simulations and quenching performed during directional solidification. The phase transition sequence of grey cast iron was determined as L → L + γ → L + γ + G → γ + G → P (α + Fe3C) + α + G. The graphite can be formed in three ways: directly nucleated from liquid through the eutectic reaction (L → γ + G), independently precipitated from the oversaturated γ phase (γ → γ + G), and produced via the eutectoid transformation (γ → G + α). The area fraction and length of graphite as well as the primary dendrite spacing decrease with increasing cooling rate. Type-A graphite is formed at a low cooling rate, whereas a high cooling rate results in the precipitation of type-D graphite. After analyzing the graphite precipitation in the as-cast and transition regions separately solidified with and without inoculation, we concluded that, induced by the inoculant addition, the location of graphite precipitation changes from mainly the γ interdendritic region to the entire γ matrix. It suggests that inoculation mainly acts on graphite precipitation in the γ matrix, not in the liquid or at the solid–liquid front.

Microstructures and Properties of High Performance Cast Irons Applied in Automobile Flywheels

High performance cast iron (HPCI) with improved mechanical properties and balanced thermal conductivity is a strong candidate to replace ductile iron in the application of automobile flywheel. In this work, the relationship between microstructures and properties, including mechanical and thermal properties, of the grey cast iron were investigated by analysing some commercial flywheels. The results showed that the content of graphite was dependent on the content of carbon in the grey cast irons, and the simulation results indicated that most of carbon directly formed into graphite at room temperature (RT). High ultimate tensile strength (UTS) is caused by low area fraction and short length of the graphite. The thermal conductivity increased with increase of the area fraction of graphite. The short length of graphite would also contribute to thermal conductivity since a large number of the short graphite flakes formed under the circumstance of the similar area fraction of graphite. In order to get HPCI, the microstructures with a moderate area fraction and short length of graphite should be controlled.