Effect of long-term service exposure on microstructure and mechanical properties of Alloy 617

Materials and Design (Impact Factor: 3.5). 05/2011; 32(5):2695-2700. DOI: 10.1016/j.matdes.2011.01.017


The present work was carried out to investigate the effect of long-term service exposure on microstructure and mechanical properties of a gas turbine hot gas path component, made of Alloy 617. The results showed significant service-induced microstructural changes, such as excessive grain boundary Cr-rich M23C6 carbides formation and some oxidation features in the exposed material in compare with the solution-annealed material. Also it was found that the yield strength and hardness of the alloy have increased while the ductility of the alloy has decreased. In the similar test conditions, the stress-rupture life of the exposed alloy decreased considerably compared to the solution-annealed sample, which could be attributed to the microstructural degradation, especially formation of continuous M23C6 carbides on grain boundaries.Research highlights► The major microstructural degradation is grain boundary M23C6 carbides formation. ► The major mechanical properties degradation is decreasing in ductility of the alloy. ► Formation of continuous carbides along GBs reduced the rupture life of the alloy.

Download full-text


Available from: Mohammad Akbari Garakani, Jan 03, 2014
151 Reads
  • [Show abstract] [Hide abstract]
    ABSTRACT: The microstructure evolution and its influence on the mechanical properties are investigated in a hot-corrosion resistant Ni-based superalloy during long-term thermal exposure. It is found that the tertiary γ′ phase disappears and the secondary γ′ phase coarsens and coalesces gradually, which acts as the main reason for the decreasing of strength at both room temperature and 900 °C. During exposure, the grain boundary coarsens from discontinuous to half-continuous and finally to continuous structure. The optimum half-continuous grain boundary structure composed of discrete M23C6 and M3B2 wrapped by γ′ film leads to the elongation peak at room temperature in the thermally exposed specimens. At 900 °C, the increase in the elongation is attributed to the much softer matrix and the formation of microvoids. The behavior of primary MC decomposition is a diffusion-controlled process. During exposure, various derivative phases including M23C6, γ′, η, M6C and σ sequentially form in the decomposed region. Primary MC decomposition and the precipitation of σ phase have little effect on the mechanical properties due to their low volume fractions.
    Materials and Design 08/2012; 39:55–62. DOI:10.1016/j.matdes.2012.02.020 · 3.50 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: An added second solution heat treatment was conducted to investigate its effects on the microstructures and stress-rupture properties of GTD-111. The microstructures were analyzed by scanning electron microscope after each step of heat treatments. The stress-rupture life of GTD-111 dramatically increases from about 180 to 288 h at 871 °C/310 MPa after adding a second solution heat treatment. The added second solution heat treatment promoted the solution of γ–γ′ eutectic into γ matrix, and facilitated the nucleation and precipitate of the secondary γ′ particles. The distribution of γ′ phase becomes much denser, the width of γ matrix channel is also reduced, and the volume fraction of γ′ phase significantly increases from about 29.3% to 44.2%. The improved stress-rupture life is primarily due to the increased volume fraction of γ′ phase. The carbides mainly consist of MC and a small amount of M23C6, which may prevent the dislocation moving and/or grain boundary sliding, and further improve the stress-rupture properties of GTD-111.
    Materials and Design 03/2013; 45:308–315. DOI:10.1016/j.matdes.2012.09.011 · 3.50 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: This paper investigates the cyclic oxidation and hot corrosion behavior of Inconel 617 at elevated temperatures. The substantial role of alloying elements with respect to oxidation and hot corrosion were analyzed with respect to corrosion kinetics, surface morphology and X-ray analysis of the oxide scales formed. The cumulative mass change shows that the presence of V2O5 in salt mixture plays predominant role in corrosion attack. Consistency of oxide scale, rich in Cr2O3, NiO, Al2O3 and NiCr2O4 was confirmed through X-ray analysis. Inconel 617 has good oxidation resistance and prone to corrosion attack at elevated temperatures due to the presence of vanadium in salt mixture which accelerates hot corrosion.
    Materials and Manufacturing Processes 07/2014; 29(7). DOI:10.1080/10426914.2014.901530 · 1.63 Impact Factor
Show more