一种细晶铸造镍基高温合金的组织与力学性能

MICROSTRUCTURE AND MECHANICAL PROPERTIES OF A Ni-BASED SUPERALLOY WITH REFINED GRAINS

通过传统铸造方法和细晶铸造工艺制备一种铸造镍基高温合金的6种不同形态与尺寸的晶粒.结果表明,细晶铸造工艺制备的样品心部为0.5 mm左右的等轴晶,外部为柱状晶.相比传统铸造方法,细晶铸造工艺获得的晶粒较为细小.g'相和碳化物随晶粒尺寸减小而变得细小.室温拉伸性能和550℃下高周疲劳性能随晶粒尺寸降低而提高;在760℃和应力662 MPa条件下,合金的持久性能随晶粒尺寸减小而增加;但在982℃和应力186 MPa条件下,合金的持久性能随之降低.细化晶粒提高了合金的中、低温力学性能,但对其高温力学性能不利.

A new Ni-based superalloy with the refined grains is to be used in industrial and aircraft turbines because of its high strength and excellent fatigue resistance at lower and medium temperatures （500-800 ℃）. The grains with six different sizes have been made by decreasing the pouring temperature from 1460 to 1480 ℃ then 1500 ℃ and adding refiner to alloy and planting seed on the surface of mold. The size of equiaxed crystal grain is reduced to 0.5 mm in the center part of specimen with the colunmnar crystals in the outside of specimen made by the refining process which is finer than those of traditional process. It has been found that γ′ phase and carbide are finer in refined grains than those in the coarse grains made by decreasing the pouring temperature. The room-temperature tensile properties and high cycle fatigue properties of tested alloy are improved with decreasing grain size. The stress-rupture properties are increased under the conditions of 760 ℃ and 662 MPa while are decreased with decreasing the grain size. The grain structure and size are refined by the refining process that dominated the excellent mechanical properties of tested alloy at lower and medium temperatures. However, it is not good for the mechanical properties at high temperatures.