Hot Corrosion of Superalloys in Boilers for Ultra-Supercritical Power Plants

The coal-based power plants have been plagued by twin problems—low thermal efficiency and emission of high level of pollutants into the environment. Over the last few decades, attention was paid by researchers worldwide to overcome these problems and to design, build, and operate coal-based plants with improving efficiency levels and reducing emission levels. Operating the power plants with higher levels of steam temperature and pressure was adopted as the direction toward achieving the needed improvements. The requirement to operate the plants with increasingly higher levels of temperature and pressure made it necessary to design the components with superalloys. Hot corrosion then becomes a major design consideration, particularly for superheaters and reheaters. Thus, it becomes important to study the hot corrosion behavior of candidate superalloys. The present chapter attempts to review the work done over the last two decades to understand the hot corrosion behavior of superalloys in the context of their use in advanced coal-based power plants

Effect of Laser Shock Peening without Coating on Grain Size and Residual Stress Distribution in a Microalloyed Steel Grade

This study aimed to identify the optimal combination of wavelength and laser pulse density to achieve the optimal pulse pressure that can induce the maximum compressive residual stress at the subsurface of microalloyed steel. For this, laser shock peening without coating (LSPwC) was performed on microalloyed steel samples at the fundamental wavelength (1064 nm) with pulse densities of 3, 6, 9, and 12 GW/cm2 and at the second harmonic wavelength (532 nm) with pulse densities of 3, 6, and 9 GW/cm2. The residual stress distributions were studied to a depth of 500 µm in the laser-treated samples. Tensile residual stress was observed at the surface of laser-peened specimens in both wavelength conditions (1064 and 532 nm). The significant impartment of compressive residual stress across the depth was achieved at the fundamental wavelength (1064 nm). The maximum compressive residual stress was attained with a laser pulse density of 9 GW/cm2 in the 1064nm wavelength condition. The optical micrographic analysis in the subsurface regions of the LSPwC specimen at 1064 nm and 9 GW/cm2 shows evidence of a high degree of plastic deformation. Electron backscatter diffraction (EBSD) analysis shows that there is grain refinement due to plastic deformations in samples subjected to the fundamental wavelength. Microhardness distribution analysis across the subsurface region shows work-hardening effects in the laser-processed samples in the 1064 nm condition. This study also shows that there is an indication of a thermal softening effect in the samples treated with the 532 nm wavelength, and it is correlated with lower compressive residual stress across the depth

Effect of Laser Shock Peening without Coating on Grain Size and Residual Stress Distribution in a Microalloyed Steel Grade

This study aimed to identify the optimal combination of wavelength and laser pulse density to achieve the optimal pulse pressure that can induce the maximum compressive residual stress at the subsurface of microalloyed steel. For this, laser shock peening without coating (LSPwC) was performed on microalloyed steel samples at the fundamental wavelength (1064 nm) with pulse densities of 3, 6, 9, and 12 GW/cm2 and at the second harmonic wavelength (532 nm) with pulse densities of 3, 6, and 9 GW/cm2. The residual stress distributions were studied to a depth of 500 µm in the laser-treated samples. Tensile residual stress was observed at the surface of laser-peened specimens in both wavelength conditions (1064 and 532 nm). The significant impartment of compressive residual stress across the depth was achieved at the fundamental wavelength (1064 nm). The maximum compressive residual stress was attained with a laser pulse density of 9 GW/cm2 in the 1064nm wavelength condition. The optical micrographic analysis in the subsurface regions of the LSPwC specimen at 1064 nm and 9 GW/cm2 shows evidence of a high degree of plastic deformation. Electron backscatter diffraction (EBSD) analysis shows that there is grain refinement due to plastic deformations in samples subjected to the fundamental wavelength. Microhardness distribution analysis across the subsurface region shows work-hardening effects in the laser-processed samples in the 1064 nm condition. This study also shows that there is an indication of a thermal softening effect in the samples treated with the 532 nm wavelength, and it is correlated with lower compressive residual stress across the depth

Synthesis and characterisation of graphene-reinforced AA 2014 MMC using squeeze casting method for lightweight aerospace structural applications

The need for lightweight materials towards aerospace has increased prominently. This paper focuses on introducing a novel reinforcement mixture of graphene with Al 2014 powder synthesised through ball milling technique. The synthesized powder was utilized as a reinforcement to fabricate Al 2014 based MMCs through squeeze casting technique. The results exhibited that Al 2014 mixture with embedded and interlocked 2D-Grnp (2.517 g/cm3) matched the density of the matrix metal (2.771 g/cm3) that facilitated homogeneous dispersion of 2D-Grnp and solved the dispersion problems during stir casting. As a result, AA 2014 embedded with 2D-Grnp acted as a carrier to homogeneously disperse combined with the squeeze casting process leading to the production of homogeneously reinforced MMC. This can be considered as a potential fabrication route for the launch vehicle super lightweight fuel tank (SLWT) structural application. The final casted plate after T6 heat treatment with 0.5 wt% 2D-Grnp exhibited an improved tensile strength of 361 MPa (52% higher than the monolithic 2014 aluminium alloy) with total elongation of 21% and improved hardness of 119 HRB (45.5 % increase). Furthermore, SEM and TEM results exhibited that squeeze casting led to enhanced interfacial bonding between the 2D-Grnp and Al 2014