In the present study, the influence of B content (0–4.69 at

The depth dependent hardness, referred to as indentation size effect (ISE) has gained considerable attention. ISE is attributed to the strain gradient caused by the inhomogeneous strain distribution beneath the indenter tip. The depth dependence of hardness is phenomenologically accounted using an appropriate length scale parameter. The Unified model is one such model that is built on Nix–Gao’s model and focuses on integrating various length scale parameters resulting from both microstructural and geometrical effects. One aspect of the current work is to assess the applicability of the Unified model to a material like bulk Nickel with a history of cold work. Also, the physics of ISE in metals can be related to the dislocation mean free path influenced by strengthening mechanisms. Past attempts are scarce to quantify the ISE through the microstructure variables. In the present work, an attempt has been made to simulate the nanoindentation test using a dislocation density based constitutive model. The objective of this study is to establish a correlation between the equivalent plastic strain resulting from deep depth indentation (which does not exhibit a size effect) and an equivalent dislocation density. The dislocation density here serves as a state variable that describes the microstructure-dependent mechanical behaviour. The modified KME, a dislocation density-based model, is incorporated as a user subroutine in a commercial finite element solver. It has been proven to accurately predict the indentation behavior at substantially large depths, which aligns well with the predictions of the Unified model or experimental observations. The good correlation between the value of effective dislocation density and equivalent plastic strain in the plastic zone underneath the indenter assures to extend the use of dislocation density as a state variable to predict ISE.

In this study we focus on understanding the influence of tungsten (W) content, heat treatment and grain size on the corrosion behaviour of Ni-W coatings. Using pulse and pulse reverse electrodeposition techniques, Ni-W coatings with different W contents (3, 7.5, 12, 17, 20 and 25 at.%) were deposited from a standard ammonia-citrate bath. Coatings were heat treated at 700 degrees C in vacuum for 1 h and then characterized to determine the surface morphology, grain size, and phase transformations. To evaluate the corrosion performance of the coat-ings, potentiodynamic polarization tests were performed in 0.6 M NaCl solution. Polarization test results indi-cated that as-deposited Ni-W coatings had better corrosion resistance compared to heat treated coatings. In the as-deposited condition, corrosion resistance increased up to 17 at.% W. However, further addition of W decreased the corrosion resistance due to high volume fraction of triple junctions and intercrystalline regions. On the other hand, heat treated coatings suffered from micro-galvanic corrosion due to the precipitation of Ni4W and NiW phases, and therefore showed higher corrosion rates compared to as-deposited coatings. The changes observed in the corrosion behaviour of as-deposited and heat treated Ni-W coatings were rationalized based on surface composition, mixed potential theory, and triple junction corrosion theory.

In the present work, the dry sliding wear behaviour of electrodeposited Ni-W/SiC nanocomposite coatings after heat treatment was studied. For that purpose, Ni-14 (at%) W/SiC composite coatings with varying proportion of beta-SiC particle content were deposited using pulsed current electrodeposition and subsequently heat-treated at 500 degrees C in vacuum. The coatings were analysed for its structure, surface topography, particle content in coating and inter-particle spacing. The mechanical properties of coatings were evaluated and correlated with SiC content in the respective coating. Sliding wear tests under dry condition were carried out (at room temperature) against WC-Co disc using pin-on-disc configuration. It has been observed that the mechanical properties of nanocomposite coatings follow the rule of mixtures (ROM). The wear rate of the nanocomposite system has demonstrated a linear relationship with the inter-particle spacing of SiC particles embedded in the Ni-W matrix. Specific wear rate and friction coefficient of nanocomposite coatings were rationalised through a mathematical model based on the inverse rule of mixtures (I-ROM).

Metal matrix composites (MMC) have found wide applications in the transportation sector. But, the presence of hard particles in the MMCs causes catastrophic tool failures. The current study presents a method to select process parameters to increase the material removal rate in finish turning of Al-MMC (Al 6061, 5% SiC, 3% C) using TiN coated carbide inserts. The key aspects of the method are (a) Using the fractional factorial method for performing experiments economically (b) Using radial force instead of cutting force (c) Using frame statistics and linear spectrum of the radial cutting force signal to select process parameters. The experiments were conducted on a precision lathe. A 6-component piezoelectric dynamometer was used to measure the cutting force.

The influence of metallurgical heterogeneities such as coring and intermetallic phases on the corrosion and stress corrosion cracking behaviours of AA7075 aluminium alloy forging was examined in 3.5 wt. % NaCl solution with and without plasma electrolytic oxidation coating. Electrochemical test results demonstrated significant improvement in the corrosion resistance of the alloy after PEO coating. Stress corrosion results show that the metallurgical heterogeneities resulted in a loss in elongation of the uncoated sample in NaCl (11.5%) when compared to the one tested in air (12.9%). The loss in elongation of the uncoated sample was shown to be due to localized corrosion-assisted mechanical cracking rather than true stress corrosion based on preexposure tensile tests followed by posttest metallographic observation of the stress corrosion tested samples. This was further confirmed by the fractographic examination of the failed samples, which exhibited a typical ductile cracking morphology for all the coated and uncoated specimens.

In recent years, the thermal spray technique has emerged as the most useful method for developing a wide variety of coatings which enhance the performance and durability of engineering components exposed to diverse forms of wear. Among the thermal spray techniques, detonation spray coating (DSC) has retained its position as one of the best available techniques for obtaining dense, wear-resistant coatings. Notwithstanding the advantages of the DSC technology over other thermal spray variants, the understanding of the fundamental aspects of this technology is still extremely limited. In view of the above, a major programme has been undertaken in this laboratory to assess the parametric impact of the key DSC process variables (oxy-fuel ratio, spray distance, powder feed rate and shot frequency) on the mechanism of coating formation and the properties of the resulting coating. As a part of the above exercise, the key DSC process variables have been varied systematically employing a statistical design and the properties of the WC-12Co coatings so obtained have been evaluated. The results of such a study are presented in this paper. In particular, it has been demonstrated that useful conclusions regarding the influence of process parameters on the properties of the WC-12Co coating cannot be reached unless the scatter in the experimentally measured coating property data is also simultaneously taken into account.