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The main objective of the paper is to review the role of different burnishing techniques used in the post-coating processing of thermally sprayed coatings. The burnishing techniques discussed here are aimed at reducing the porosity and the coating surface defects for their application to combat solid particle erosion (SPE) in industrial applications such as pulverized coal burner nozzles (PCBNs). The PCBNs in thermal power plants are exposed to a high erosion rate compared to boiler tubes, due to very high velocity and the mass flux of the pulverized coal. A high surface roughness, cracks and porosity in thermally sprayed surfaces reduce their SPE resistance. The severe plastic deformation (SPD) process, known as roller burnishing, is reported to cause significant surface modifications of thermally sprayed coatings. The surface irregularities are suppressed by the burnishing tool during SPD, which consequently fills the nearby pores and valleys due to plastic deformation. This paper reviews the performance of burnishing performed by a grinding wheel-shaped tool and compares their surface characteristics or the SPE behavior with the burnishing performed by roller burnishing and the grinding process. Moreover, the impact of cryogenic burnishing on the performance of the coatings is also studied and discussed in detail.

Laser-based surface enhancement techniques improve metals’ mechanical properties. Laser Hardening (LH) and Laser Shock Peening (LSP) techniques are effective particularly well with low-alloy steel made of 34Ni-Cr-Mo6, which is a type of steel alloy that is put to use in a wide variety of fields because it possesses excellent levels of both strength and toughness. For specific applications, the laser can be shaped into line or spherical beams. On the other hand, typical industrial requirements of low alloy steel components like 34Ni-Cr-Mo6 are enhanced hardness and mechanical strength with minimum or no distortion. A 3 kW high power fiber laser with a flat top-hat beam of dimension $30\times 1$mm and a circular beam of Ø6mm are employed in this study. Investigation into the effects of repeated LSP on the microstructures and residual stress of 34Ni-Cr-Mo6 low alloy steel was also done. LSP treatment is carried out at 6.36GWcm${}^{-2}$ Laser Power Density (LPD) with different laser impacts, i.e. single and double, by keeping 0% overlap along the scanning direction and perpendicular directions, respectively. The shock-peened samples were characterized in terms of residual stress measurements and microstructural evolution using different characterization techniques. A substantial improvement in compressive residual stress was observed at the hardened cross-section i.e. $\sim -260$MPa and at shock peened surface $\sim -620$MPa respectively as compared to the as-received sample ($\sim -100$MPa). LH samples showed a better result in terms of microhardness values when compared to shock peened samples i.e. for LH, the microhardness values at the cross-section were $\sim 710\pm 40$HV${}_{0.5}$ nearly 2.5 times increase in hardness. Extreme plastic deformation was found by microstructural examination of cross-sections of LSP-treated areas. Hardness was nearly marginally improved in multiple times LSP-treated samples compared to unpeened ones as a result of LSP.

A bulky Cu-Zn alloy was multi-directionally forged (MDFed) at 77 K and 300 K up to a cumulative strain of 6.0 at maximum. With increasing strain, the evolved substructure changed gradually to uniform ultra fine grains. The tendency of the microstructural evolution and its mechanism depended strongly on the MDF temperature. Mechanical twins accelerated the finer grain fragmentation by subdivision of the grains and by intersection of the twins themselves due to MDF. Twinning appeared more frequently and uniformly at 77 K than at 300 K. The average grain size obtained at a cumulative strain of 6.0 was about 17 nm at 77 K and 26 nm at 300 K. The evolution of the microstructure accompanied by mechanical twinning is precisely investigated.

An ultrafine grained (UFG) aluminum sheet was produced using severe plastic deformation (SPD) by a process known as accumulative roll bonding (ARB). Electron Back Scattered Diffraction (EBSD) method and Transmission Electron Microscopy (TEM) were utilized for characterization of the subgrain and grain structures of the processed sheets. The results indicate that different mechanisms at different levels of strain lead to the gradual evolution of ultrafine or nanocrystalline grains. Grain fragmentation as well as the development of subgrains are the major mechanisms at the early stages of ARB. Strain induced transformation of low angle to high angle grain boundaries and formation of a thin lamellar structure occur at the medium level of strain. Finally, the progressive fragmentation of these thin lamellar structures into more equi-axed grains is the dominant mechanism at relatively high strains which results in grain size reduction to submicron scale.

This work aims to investigate whether accumulative roll bonding (ARB) is an effective grain refinement technique for ultra-low-carbon steel strips containing 0.004% C. For this purpose, a number of ARB processes were performed at 500 °C, with 50% reduction in area of each rolling pass. It was found that both the ultimate grain size achieved, as well as the degree of bonding, depend on number of rolling pass and reduction of area as a whole. The mean grain size was obtained using AFM was about 130nm. The mechanical properties after rolling and cooling were obtained. Also, the fracture surfaces were studied by Scanning Electron Microscopy (SEM). It was concluded that metal's tensile strengths increased by 334% while the ductility dropped from a prerolled value of 50.5% to 2.6%. Effect of wire brushing on samples observed too. It increased on the wire brushed sheet for 7 HV. The rolling process was stopped when cracking of the edges became pronounced.

The technique of severe plastic deformation (SPD) enables one to produce metals and alloys with an ultrafine grain size of about 100 nm and less. As the mechanical properties of such ultrafine grained materials are governed by the plastic deformation during the SPD process, the understanding of the stress and strain development in a workpiece is very important for optimizing the SPD process design and for microstructural control. The objectives of this work is to present a constitutive model based on the dislocation density and dislocation cell evolution for large plastic strains as applied to equal channel angular pressing (ECAP). This paper briefly introduces the constitutive model and presents the results obtained with this model for ECAP by the finite element method.

Equal channel angular extrusion/pressing multipass simulations were carried for two routes, Route A and Route C, by using finite element code Abaqus/Explicit. Realistic parameters like strain hardening behavior of material, friction between the sample and die were considered for simulations. The strain homogeneity and deformation behavior of samples during multipass ECAE with different routes were studied. The deformation behavior of the sample processed through Route A is smooth. Accordingly strain homogeneity of the samples was more of a possibility with Route A than with Route C.

NiTi shape memory alloys were subjected to a single step severe plastic deformation via the equal channel angular pressing (ECAP). The properties were analyzed by comparing the transformation characteristics for sections across the thickness of the deformed sample, with focus on the deformation gradient in the outer layers of the materials and the front surface that gradually engages in the deformation. A gradient related to the crystallinity and the state of stress was observed across the thickness of the deformed sample.

Severe plastic deformation of a Ti${}_{50}$Ni${}_{25}$Pd${}_{25}$ high-temperature shape memory alloy yields a nanoscale mixture of an amorphous phase and retained lamellae of the parent B19 martensite. The thermal stability of the deformed martensite is significantly enhanced. Upon heating, B2 austenite occurs within the martensite and by crystallization of the amorphous phase, concomitant with recovery and the formation of an ultrafine grained structure. In the small grains, the B2 austenite to B19 martensitic transformation is shifted to lower temperatures and incomplete.

Recently, severe plastic deformation processes have been the essence of metal forming researches to produce ultrafine-grained materials. Twist Extrusion is one of the most unprecedented methods developed in recent years, but has some deficiencies. The main one is the microstructure and mechanical heterogeneity, occurring after twist extrusion. Performing rolling as a conventional forming technique was suggested as a solution in this paper. It not only decreased the grain size, but also reduced the mechanical heterogeneity, and improved the grain size distribution. Employing the twist extrusion process on pure copper samples was carried out using a twisted die with 60° die angle, and the samples were processed through rolling subsequently. The results demonstrated that employing the rolling process enhanced grain size homogeneity and bulk strength.

Constrained groove pressing (CGP) is an attractive severe plastic deformation technique capable of processing ultrafine grained/nanostructured sheet materials. The deformation behavior of pure aluminum during constrained groove pressing is investigated by carrying out a two-dimensional finite element analysis (FEA). FEA predicted deformation behavior observed during each stages of pressing indicated almost negligible deformation in flat regions, whereas the inclined shear regions revealed diverse deformation characteristics. The plastic strain distributions unveiled inhomogeneous strain distribution at the end of one pass. Detailed examination of plastic strain evolution during CGP along various sections divulged superior strain distribution along middle surfaces when compared to top and bottom surfaces. The degree of strain homogeneity is evaluated quantitatively along different regions of the sheet and is correlated to the deformation characteristics. Load–stroke characteristics obtained during corrugating and flattening of sheets exhibited three stages and two stages behavior, respectively. The results obtained from the analysis are experimentally validated by processing pure aluminum sheets by CGP and the measured deformation homogeneity is benchmarked with FEA results.

In sheet fine-blanking process, severe plastic deformation localized in a narrow shear band near blanking clearance, and ductile fracture present at the final stage. Since the combinations of large nonlinear strain localization, displacement discontinuity and ductile fracture, a new ductile fracture initiation criterion model and elasto-plastic FEM are used to simulate localized severe plastic deformation. The distributions and developing trends of effective strain and damage are investgated, and an experiment also performed to research the forming mechanism and process parameters.