Mechanism of M23C6 → M7C3 carbides reaction of Cr35Ni45Nb type alloy during carburization

The carbide transformation of Cr35Ni45Nb type alloy during service has been investigated in the present work. The primary carbide of the as-cast Cr35Ni45Nb type alloy is M _7 C _3 (M is mainly Cr element) and NbC, which transformed into M _23 C _6 type carbides (M is mainly Cr element) and G phase(Ni _16 Nb _6 Si _7 ) after service, respectively. The G phase and M _23 C _6 carbides mix together and grow up with each other during service. After carburization, the crystal structure of M _23 C _6 type carbide changes again and transforms into M _7 C _3 type carbide. The mechanism of M _23 C _6  → M _7 C _3 carbide reaction is an in situ transformation; the M _7 C _3 type carbide preferentially nucleates at the interface of M _23 C _6 / γ and grows toward the M _23 C _6 type carbide interior. With the diffusion of free carbon atoms into the M _23 C _6 type carbides, the M _23 C _6 type carbides are gradually surrounded by the M _7 C _3 type carbides until they are completely changed into M _7 C _3 type carbides

High Temperature Oxidation and Wear Behaviors of Ti–V–Cr Fireproof Titanium Alloy

The high temperature oxidation and wear behaviors of Ti–35V–15Cr–0.3Si–0.1C fireproof titanium alloy were examined at 873 and 1073 K. The oxidation weight gain after oxidation at 1073 K for 100 h was significantly larger than that at 873 K. Based on the analyses of the oxidation reaction index and oxide layer, the oxidation process at 1073 K was mainly controlled by oxidation reaction at the interface between the substrate and oxide layer. Dry sliding wear tests were performed on a pin-on-disk tester in air conditions. The friction coefficient was smaller at 1073 K than that at 873 K, while the volume wear rate at 1073 K was larger due to formation of amount of oxides on the worn surface. When the wearing temperature increased from 873 to 1073 K, the wear mechanism underwent a transition from a combination of abrasive wear and oxidative wear to only oxidative wear

Microstructure damage of directionally solidified alloy turbine blade after service

Turbine blades are the most demanding components in aircraft engines, and their performance is related to the safety of the whole engine. Due to the complex service environment and harsh service conditions of blades, various types of damage cannot be prevented in service. Therefore, it is of great engineering and economic significance to study the service damage of blades. In this paper, the directional solidification alloy turbine blade after actual service was selected as the research object. The cross section position of 80% upper height of the blade was intercepted, and the qualitative and quantitative microstructure analysis was carried out by SEM and EDS analysis. The results show that there are two different types of γ' phases in this leaf. One kind of γ' phase has small size and regular shape, the other has large size and irregular shape. The degree of microscopic damage among different parts of the blade is characterized with the help of dimensional distribution characterization of the γ' phase of each part, combined with the analysis of hardness testing of each part of the cross-section.The results show that the service conditions of different parts are different, and the degree of microstructure damage is different. In addition, matrix crack and coating crack in some parts of blade are summarized and analyzed