Thermal stability of the structure of a high-temperature nickel alloy fabricated by two different technologies

Abstract

High-temperature treatment of the melt (HTTM) is a very simple and available technique for stabilizing and improving the service properties of parts. It consists in heating the melt to a certain critical temperature, a hold, and cooling. The present paper is devoted to the effect of HTTM, the standard heat treatment, and long isothemaa] holds at the service temperatures on the structure and properties of castable high-temperature nickel alloy ZhS6U.

Microstructure and stress rupture property of Ni-based monocrystal superalloy with melt superheating treatment

“…Therefore, it is believed that the solidification microstructure variation for the elevated superheating temperature cannot be owing to the external solidification parameter but should be attributed to the internal melt characteristic change. It has been found that Ni 3 Al-like cluster, residual MC carbide and other highmelting particle still exist in the Ni-based superalloy melt near the liquidus [8][9][10][11][12][13][14]. With the melt temperature increase, those clusters will decrease in their sizes and even disappear, which leads to the increase of composition uniformity.…”

“…With the melt temperature increase, those clusters will decrease in their sizes and even disappear, which leads to the increase of composition uniformity. The melt at this kind of equilibrium or near equilibrium state has increased supercooling degree and compressed temperature range for crystallization [10][11][12][13][14]. It is very important that due to the so-called "heredity effect", the melt will remain its high temperature characteristic to a certain extent even when it is cooled down [3][4][5][7][8][9][10][11][12][13][14].…”

“…tallization. It is reported that with HTTM method, the dendrite and the ␥ precipitate are all refined and the stress rupture life for ZhS6U superalloy under 975 • C/230 MPa can be increased by about 30% [14].…”

“…It has been shown that the melt structure, the solidification microstructure and the performance of Al-Si alloy, Nd-Fe-B alloy and superalloy can be significantly modified by the melt overheating treatment [5][6][7][8][9]. The researchers in Russia have studied the superalloy melt structure in detail and have put forward a technique named high temperature treatment of melt (HTTM) for high-performance superalloy casting [10][11][12][13][14]. It has been pointed out that the melt just above the liquidus temperature is generally in nonequilibrium state consisting of different kinds of atom clusters.…”

Modeling of changes in heat resistance of nickel-based alloys using Bayesian artificial neural networks

“…Характерные точки перегибов и угол наклона участка с интенсивными убыванием σ зависят от структурных изменений, происходящих в сплавах в период испытаний. Наши исследования [12,13] и результаты других ученых [14 -21] позволяют представить общий порядок этих структурных изменений: после литья и термической обработки структура монокристаллических ЖНС состоит из γ-никелевой матрицы, основной упрочняющей мелкодисперсной γʹ-вторичной фазы и эвтектики (γ + γʹ). Температура и приложенные во время испытаний нагрузки приводят к существенным структурным изменениям: образуется рафт-струкутра и возникают дислокации; кубоидные выделения основной упрочняющей фазы коагулируют, происходит рост их блоков; при выдержках свыше 1100°С количество γʹ-вторичной фазы существенно снижается; округлые выделения γ + γʹ эвтектики заменяются на колонии мелких частиц; структурные изменения приводят к возникновению и росту охрупчивающих топологически плотно упакованных фаз, типа µ, σ, Лавеса и других.…”