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Cemented carbide tools are extensively used in the zipper industry, including shearing of a pre-formed Cu15Zn wire into individual zipper elements. Although the work material is significantly softer than the tool, wear is the life limiting factor for the tools and is considered to be of tribochemical nature. So far it has not been explained, however, it is known that the wear rate of uncoated, as well as CrC and CrN coated, cemented carbide increases dramatically when Zn is omitted from the Cu alloy. In this paper, worn tool surfaces, including any transferred material, were studied to investigate the tribochemical wear mechanism in detail. Material transfer occurred onto all tool surfaces. Cu and Zn were separated on the sub-micron scale, and preferential transfer of one of the constituents was observed. This is reflected in the outermost surface of the sheared element, which shows a homogeneous composition elsewhere. Oxidation was observed of all tool surfaces, which indicates elements of oxidative wear. Further, any Zn transferred to the tool surfaces was oxidized. Thus, it is suggested that the presence of Zn reduces the oxygen available and consequently reduces the oxidation rate of the tool surfaces, leading to the protective effect previously observed. © 2024 The Authors

Two different grades, WC-20 vol.% Ni and WC-20 vol.% Co cemented carbides, respectively were systematically investigated concerning their microstructure, binder composition, and corrosion behavior. SEM-EBSD analysis verified that both grades have similar WC grain sizes (0.9–1.1 μm). AES analysis confirmed that the binder phase of the respective grade is an alloy of Ni-W and Co-W and that the concentration of W in the Ni- and Co-binder is 21 and 10 at. %, respectively. In synthetic mine water (SMW), the EIS behavior of WC-Ni(W) at the open circuit potential (OCP) conditions was studied for different exposure periods (up to 120 h). The EIS data fitting estimates low capacitance and high charge transfer resistance (Rct) values, which indicate that the passive film formed on WC-Ni(W) is thin and exhibits high corrosion resistance. At the OCP and potentiostatic-passive conditions, SEM investigations confirm the uncorroded microstructure of the WC-Ni(W). The AR-XPS studies confirmed the formation of an extremely thin (0.25 nm) WO3 passive film is responsible for the high corrosion resistance of WC-Ni(W), at OCP conditions. However, above the transpassive potential, the microstructure instability of WC-Ni(W) was observed, i.e., corroded morphology of both WC grains and Ni(W) binder. The electrochemical parameters, Rct, corrosion current density, and charge density values, confirmed that the WC-Ni(W) is a far better alternative than the WC-Co(W) for application in SMW.

Electron beam powder bed fusion (PBF-EB) is used to manufacture dense nickel titanium parts using various parameter sets, including the beam current, scan speed, and postcooling condition. The density of manufactured NiTi parts is investigated in relation to the linear energy input. The results imply that the part density increases with increasing linear energy density to over 98% of the bulk density. With a constant energy input, a combination of low power and low scan speed leads to denser parts. This is attributed to lower electrostatic repulsive forces from lower number density of the impacting electrons. After manufacturing, the densest parts with distinct parameter sets are categorized into three groups: 1) high power with high scan speed and vacuum slow cooling, 2) low power with low scan speed and vacuum slow cooling, and 3) low power with low scan speed and medium cooling rate in helium gas. Among these, a faster cooling rate suppresses phase transformation temperatures, while vacuum cooling combinations do not affect the phase transformation temperatures significantly. Herein, all the printed parts exhibit almost 8% pseudoelasticity regardless of the process parameters, while the parts cooled in helium have a higher energy dissipation efficiency (1 − η), which implies faster damping of oscillations. © 2023 The Authors. Advanced Engineering Materials published by Wiley-VCH GmbH.

In this study,microstructure and mechanical characterization of as-built Hastelloy X (HX) samples produced by laser powder bed fusion (LPBF) process and post-heat-treated samples were investigated. Two sets of samples, horizontal and vertical to build direction, were considered in as-built condition to understand the effect of build direction and two solution heat-treatment temperatures, 1177°C and 1220°C, followed by fast cooling were considered to study the effect of solution heat-treatment temperature on microstructure and mechanical properties. Microstructure characterization of as-built sample horizontal to build direction revealed a typical multi-layer molten pool boundaries and the sample vertical to build direction revealed multi-layered and multi-tracked molten pool boundaries. Electron backscatter diffraction results reveal a disrupted epitaxial grain growth for the as-built samples vertical to build direction whereas equiaxed grain structure with varying twin grain boundary fractions was observed for heat-treated HX samples. As-built LPBF HX samples exhibit higher mean hardness and yield strength than post-heat-treated samples. Higher elongation and lower yield strength were observed for the sample solution treated at 1220°C as compared to the sample solution annealed at 1177°C. Microstructural evolution at 20% engineering strain for the exact positions before the tensile test was presented for solution treated at 1220°C samples, which reveals distinct slip lines within each grain as well as increased dislocation density at grain boundaries. © 2022 The Authors. Published by Elsevier B.V.

Ti-35Nb-7Zr-5Ta (TNZT) alloy has been fabricated by selective laser melting (SLM) at different build orientations with respect to the base plate and the resulting disparities in the grain shape, size, preferred orientations and lattice strains have been determined. Potentiodynamic polarization tests performed under in vitro conditions indicated that the specimens built at 45° orientation showed the highest polarization resistance (24.5 kΩ cm2) and lowest rate of corrosion (0.23 μA cm−2) compared to the specimens built at other orientations. The corrosion behaviors of the SLM specimens have been correlated with their microstructural features and further compared with that of its spark plasma sintered (SPS) counterpart and commercial alloys such as Ti6Al4V and Ti6Al7Nb. Electrochemical impedance spectroscopy and potentiostatic measurements have revealed that the passive film forming on the TNZT sample at 45° orientation is highly stable and more protective than that of the other samples. Auger electron spectroscopy has confirmed that both Ti and Nb participate actively in the passive film formation on the SLM TNZT alloy.

High-density powder metallurgy (PM) components are required for high-performance applications. Liquid phase sintering (LPS) is one such method to improve the densification, especially the master alloy route is preferred due to the flexibility in tailoring the alloying contents. In this study, gas atomised Ni-Mn-B master alloy powder of size fraction < 45 µm was admixed with water atomised iron and Mo-prealloyed powder. During sintering, there was a significant densification due to LPS where the liquid formation occurred in two stages, one from the master alloy melting and another from the eutectic liquid formation, enabling densities > 95%. The microstructural investigation revealed that the surface densification was achieved after sintering in H2 containing atmosphere. Capsule free hot isostatic pressing was performed on these samples to achieve full density. This approach of combining LPS and capsule free hot isostatic pressing demonstrates the potential in reaching full densification in high-performance PM steel components.

Abstract Al0.1CoCrFeNi-high entropy alloy (HEA) /tungsten carbide (WC)metal matrix composite was successfully prepared by mechanical alloying and subsequent spark plasma sintering. The different volume fraction of WC was distributed evenly by varying the powder milling parameters from gentle milling (~1.37% WC) and intensive milling (~14.27% WC). Sintering of gently milled powder has resulted in the evolution of three-phased microstructure: α-fcc and Cr- rich σ-phase with some WC-phase distributed in the HEA matrix. On the other hand, the sintering of intensively milled powder has resulted in a two-phased microstructure: α-fcc phase with even and dense distribution of WC-phased particles without any Cr- rich σ-phase. The absence of σ-phase is attributed to a complete alloying of Cr in the HEA matrix. Microhardness analysis and compression test indicate that a ~ 13% difference in WC fraction has resulted in an enhancement in hardness (46%) and compressive strength (~ 500 MPa).

Al0.1CoCrFeNi high-entropy alloy (HEA) was synthesized successfully from elemental powders by mechanical alloying (MA) and subsequent consolidation by spark plasma sintering (SPS). The alloying behavior, microstructure, and mechanical properties of the HEA were assessed using X-ray diffraction, electron microscope, hardness, and compression tests. MA of the elemental powders for 8 h has resulted in a two-phased microstructure: α-fcc and β-bcc phases. On the other hand, the consolidated bulk Al0.1CoCrFeNi-HEA sample reveals the presence of α-fcc and Cr23C6 phases. The metastable β-bcc transforms into a stable α-fcc during the SPS process due to the supply of thermal energy. The hardness of the consolidated bulk HEA samples is found to be 370 ± 50 HV0.5, and the yield and ultimate compressive strengths are found to be 1420 and 1600 MPa, respectively. Such high strength in the Al0.1CoCrFeNi HEA is attributed to the grain refinement strengthening.

The wear of metal cutting tools is known to take place by the combined and simultaneous effects of several wear mechanisms. Knowledge of the relative contribution of the individual wear mechanisms is required to understand and predict the tool wear during cutting different workpiece materials and alloys. It has been shown previously that machining two heat resistant superalloys, alloy 718 and Waspaloy, leads to distinctively different tool wears. Even though the subject has been addressed in various studies, there are still open questions regarding the underlying reasons for the differing tool wear rates. In particular, the relative contributions of diffusion/dissolution when machining the two alloys have not been addressed so far. Therefore, a qualitative comparison of the chemical interaction between the tool material and the two superalloys was made by using diffusion couple tests. The aim was to mimic the high temperatures and intimate contact between workpiece and tool material at the tool rake and flank faces during cutting under controlled and static conditions. The obtained results suggest that it is unlikely that differences in flank wear rate when machining the two superalloys are caused by significantly varying magnitudes of tool atoms dissolving into the respective workpiece. Analysis of the tool/superalloy interfaces in the diffusion couples revealed diffusion-affected zones of similar size for both tested superalloys. Increasing test temperature led to enhanced interdiffusion which suggests an increase in tool wear by diffusion/dissolution for higher cutting temperature. For alloy 718, the higher test temperature also led to depletion of carbon together with formation of tungsten within the tool in close vicinity to the interface with the superalloy.