ABSTRACT We demonstrated the systematic investigation of the graphene addition on the microstructural behaviour and concurrent thermoelectric properties of water-atomized p-type BiSbTe (BST)- based alloy using mechanical ball milling, and followed through the spark plasma sintering to fabricate a bulk compact specimen. X-ray diffraction results confirm the single phase of BST. The fracture surface of both specimen exhibits the homogenous distribution of grains with irregular shapes in a random alignment. The graphene in the BST provides an extra carrier transport leading to an increment in the carrier concentration (n) resulting in higher electrical conductivity (σ) for the BST + Graphene composite. The interface between two-dimensional (2D) graphene and bulk BST provides a larger degree of phonon scattering leading to a maximum reduced thermal conductivity (к) of 0.8 W m−1K−1 compared to pristine- BST (0.9 W m−1K−1) results in a maximum figure of merit (ZT) 1.1 at 400 K.

ABSTRACT In this study, water-based precursor solutions with citric acid as the chelating agent were prepared, and the effect of the pH of the precursor solutions on the morphology and microstructure of the Li1.3Al0.3Ti1.7(PO4)3 (LATP) coating layer was investigated. A clear precursor solution was prepared and its colour changed depending on the pH of the solution, suggesting that citric acid effectively formed chelate complexes composed of Li, Al, Ti and P ions. The scanning electron microscopy and energy-dispersive X-ray spectroscopy mapping analyses showed that a low pH resulted in a homogeneous LATP coating layer with a fine particle size and less dense morphology. When the pH value was increased, dense and enhanced surface coverage was obtained, whereas an inhomogeneous atomic distribution was confirmed in the LATP coating. The LATP-coated LiCoO2 (LCO) cathode exhibited enhanced specific capacity retention compared to that of the pristine LCO cathode.

ABSTRACT A TiCN-Co-Cr3C2-based cermet, with the addition of 5wt. % and 10wt. %Si3N4 and a reference sample without Si3N4 addition were prepared by the spark plasma sintering technique. The average hardness and fracture toughness of the 90TiCN-5Co-5Cr3C2(SN00) cermet-sintered specimens were e14.85±3.11 GPa and 6.78±0.61 MPaÖm, respectively. The cermet composition 85TiCN-5Co-5Cr3C2-5 wt. % Si3N4(SN05) enhanced the hardness and fracture toughness to 20.90±0.825 GPa and 7.23±0.45 MPaÖm, respectively. Further addition of 10 wt%Si3N4 with 80TiCN-5Co-5Cr3C2(SN10) decreased the hardness value to 16.18±0.279 GPa due to a decrease in the density of defects. However, the fracture toughness steadily increased to 9.34±3.10 MPaÖm. The cermet composition 85TiCN-5Co-5Cr3C2-5Si3N4 (SN05) showed an appreciable improvement in hardness and toughness values due to the formation of a core-rim structure, with the core consisting of TiCN and the rim with TiN, TiO2, TiSi, Co2C, CrN and Cr2Si.

ABSTRACT Owing to its processing freedom, additive manufacturing has emerged as a promising material processing method for Fe–Si alloys. In this process, the melt pool fused by selective laser undergoes rapid cooling, which results in non-equilibrium solidifications. Therefore, it is essential to systematically investigate the relationship between process parameters, microstructure and magnetic properties of the Fe–Si alloys manufactured by the L-PBF process. However, the conventional experimental approaches require time-consuming and costly procedures and a great deal of trial and error. In this regard, an efficient and cost-effective tool is needed to investigate the effect of process parameters on the microstructure and magnetic properties under a wide range of process conditions. In this study, the processing parameter correlations were conducted based on the statistical methods using the design of experiments. Through this method, the effect of process parameters on various properties, including relative density, coercivity and saturation magnetisation, was systematically investigated.

ABSTRACT A significant enhancement in the coercivity and grain refinement was revealed for the spark plasma sintered NdFeB magnets by doping eutectic alloy (Nd0.75Pr0.25)70Cu30 powders. The commercially available NdFeB powders were mixed with (Nd0.75Pr0.25)70Cu30 powders (0, 2 and 5 wt.%) and then consolidated by spark plasma sintering at 700°C under 50 MPa. Microstructure analysis shows that the addition of (Nd0.75Pr0.25)70Cu30 alloy reduces the formation of coarse grain zone and decreases the average Nd2Fe14B grain size by intergranular phase modification. The RE-rich phase containing Nd, Pr at the Nd2Fe14B grain boundary caused the magnetic isolation effect. Hence, the coercivity increased from 18.3 kOe for un-doped NdFeB to 20.3 and 21.6 kOe with doping content of 2 and 5 wt.%, respectively. This study provides an economic way to fabricate sintered NdFeB magnets with enhanced coercivity and homogeneous nanostructure.

ABSTRACT H13 tool steel was additively manufactured by selective laser melting (SLM). The sample printed at a higher laser scan speed exhibited higher strength and ductility than those of the sample printed at a lower speed. The samples were repeatedly exposed to a massive heat input during the SLM. The in-situ tempering effect was applied to the sample; the phase fraction is changed by varying the heat input by controlling the laser scan speed. The microstructure analysis showed that the sample printed at a higher scan speed had a higher fraction of retained austenite than at a lower speed. The former was affected by deformation-induced martensitic transformation with enhanced strain-hardening ability. This study entailed the control of process parameters to improve the mechanical properties and the productivity of SLM-printed H13 tool steel. It investigated the relationship between the laser scan speed and the phase fraction, whose effect on the mechanical properties was confirmed.

ABSTRACT In this study, dry sliding wear of AlSi0.75TiMnFeCux (x = 0, 0.25, 0.5) high-entropy alloy (HEA) produced through mechanical alloying (MA) and spark plasma sintering (SPS) was studied. The microstructure and phase evolution were examined using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The wear behaviour of HEAs was assessed by reciprocating wear monitor under a dry air atmosphere. The findings demonstrated that AlSi0.75TiMnFeCux HEAs were multiphase body-centred cubic (BCC/B2) solid solution structured with complex µ-, L21, and Laves. It was discovered that the microhardness and wear behaviour of AlSi0.75TiMnFeCux were comparable to AlSi0.75TiMnFe HEA after the addition of Cu up to 0.25 molar ratio. The maximum hardness of the AlCu0-0.5FeMnTiSi0.75 HEAs reached around 1021–1035 HV. The tribology results show that an oxidative wear in AlSi0.75TiMnFe while the mixed adhesive-abrasive wear mechanism was prominent in the AlSi0.75TiMnFeCu0.25-0.5 HEAs.

ABSTRACT Tungsten contains cemented carbide and is an industrially important material. Tungsten oxide is also used as a hardmetal; thus, there is an increased demand for nanosized and highly purified products. This has spurred considerable research interest toward developing a controlled technique for oxidising cemented carbide scraps to directly recycle them into powders. Cemented carbide is converted into tungsten oxide in an oxidising atmosphere, and is characterised as a porous powder formed by expansion during the oxidation reaction. Uniformly oxidising powdery cemented carbide during oxidation heat treatment is difficult, and tungsten oxide particles grow when oxidised at a high temperature for long durations. To study the uniform oxidation of WC–Co cemented carbide, the oxidation behaviour of powdered WC–Co was analysed by varying the temperature and atmospheric oxygen concentration. The phases of the produced oxide powder were analysed, and the specific surface area was measured to confirm the average particle size.

ABSTRACT In this study, new metamorphic alloy powder (M+) with an optimised composition of Fe-Cr-B-Mo-Nb appropriate for thermal spray process was developed by adding Mo and Nb, and the novel metamorphic alloy coating was fabricated by atmospheric plasma spray (APS) process. Thereafter, the corrosion resistances of the coatings were investigated and compared with those of commercial Fe-Cr-B based metamorphic alloy (M). The high-temperature oxidation resistance of the developed M+ powder feedstock was 2.18 times better than that of the commercial M. The in-flight oxidation occurring during APS process in M+ alloy decreased by 39.5% compared to that in M alloy. The passivation behaviour of M+ alloy was more stable than that of M alloy in a 3.5 wt% NaCl solution. The effect of adding Nb and Mo on the corrosion resistance of M+ coatings was also discussed in connection with microstructural changes.

ABSTRACT A novel, two-step, solid-state method to produce complex geometry titanium parts was investigated by combining Cold Isostatic Pressing (CIP) with Field Assisted Sintering Technology (FAST). Hydride-dehydride powders of commercially pure titanium and Ti-6Al-4V were CIP’ed into shaped compacts using silicone moulds, then further consolidated using FAST, with ZrO2 powder as a secondary pressing media. The final parts retained the complex features from the CIP moulds but were compressed in the pressing axis. Densities >99% were achieved, with optimised FAST processing parameters required for the different alloys. High hardness and fine equiaxed microstructures were observed at the edges of the parts, suggesting oxygen transfer from the ZrO2 pressing media had occurred, with more investigation needed to better understand and prevent this. Despite this, the CIP-FAST process route has been demonstrated to be a fast, low-cost and material-efficient option to produce a wide variety of complex titanium parts.