As-deposited Research Articles

Microstructure evolution and mechanical properties of Al–Cu–Mn–Cd alloy fabricated by CMT-wire arc additive manufacturing

The high-performance additive manufacturing of relatively small aluminum alloy components has been widely proven successful. However, wire arc additive manufacturing (WAAM) has always been challenging in achieving uniform microstructure and high mechanical properties when manufacturing large-sized parts. Therefore, this study used cold metal transition wire arc additive manufacturing (CMT-WAAM) to prepare Al-5.49Cu-0.4Mn-0.29Cd (ACMC) alloy to obtain a uniform microstructure and improve its mechanical properties. The results show that the as-deposited (AD) samples have an obvious layered deposited structure. The grains in the microstructure are all equiaxed crystals and a large amount of copper-rich eutectic phase precipitates at the grain boundaries. After heat treatment, the vast majority of the eutectic phase dissolves, and θ'phase, with a size of 100–200 nm, uniformly precipitates in the α-Al matrix. The ultimate tensile strength (UTS) and yield strength (YS) of the heat-treated (HT) specimen can reach 483.7 MPa and 412.3 MPa, respectively. There is no significant difference in the mechanical properties between the transverse and longitudinal directions of thin-walled samples. Based on experimental results and theoretical analysis, the strengthening mechanism and fracture mechanism of CMT-WAAM aluminum alloy were revealed. This work provides a theoretical basis for the microstructure optimization and mechanical performance improvement of ACMC alloy, which is of great significance for the high-performance preparation of large-sized components in the aerospace field.

Enhanced tribological performance of laser directed energy deposited Inconel 625 achieved through laser surface remelting

Inconel 625 (IN625) is an essential material for the manufacture of turbine blades and seals, aircraft ducting systems, engine components, and pressure valves. Laser Directed Energy Deposition (LDED) process has shown the potential to fabricate IN625 parts with superior mechanical properties and higher corrosion resistance when compared to those fabricated using conventional manufacturing techniques. However, the poor surface quality limits the practical application of LDED fabricated parts, especially in sectors that demand high tribological performance. To this end, this study focuses on improving the surface quality and tribological performance of LDED fabricated IN625 components using Laser Surface Remelting (LSR) as a postprocessing operation. The tribological performance was evaluated using a linear reciprocating ball-on-flat wear test setup. The surface roughness, remelting depth (RD), microstructure, hardness, and tribological performance (coefficient of friction and wear rate) of the remelted (RM) samples were compared with that of as-deposited (AD) samples. Microstructural characterization revealed that LSR resulted in grain refinement, reduced dendrite size, and primary dendritic arm spacing (PDAS). Laser scanning speed effects RD, dendrite size and PDAS via its effect on cooling rates. SEM + EDS analysis confirmed the presence of Laves phase in both AD and RM samples. XRD analysis of RM samples showed an increase in the amount of Laves phase. The refinement in microstructural features and the increased amount of Laves phase among the RM samples led to improvement in microhardness when compared to AD samples. Wear test results revealed a reduction in the coefficient of friction (COF) and wear rate after LSR with wear mechanism being either abrasive or delamination. Reduction in the size of dendrites and refinement in grain size are attributed to the enhanced tribological performance after LSR.

Tailoring the microstructure and mechanical properties of laser metal-deposited Hastelloy X superalloy sheets via post heat-treatment

Nickel-based superalloys are subject to severe microsegregation and exhibit anisotropic properties during laser metal deposition (LMD), which restricts their wide application in the aerospace field. Thus, post heat-treatments must be investigated to further regulate the microstructure and mechanical properties of such components. The aim is to provide a comprehensive understanding of the effects of double-stage aging (DA) and solution plus double-stage aging (SDA) heat treatments on microstructure and mechanical properties of Hastelloy X superalloy sheets fabricated via LMD. The effects of DA and SDA heat treatments on the density, residual stress, phase composition, carbides precipitation behavior, dislocation structure, grain structure, and mechanical properties of the sheets were studied and in comparison with the as-deposited (AD) samples. The results showed that the DA heat treatment yielded a significant amount of lamellar and granular phases in the interdendrites and grain boundaries, whereas the anisotropic microstructure between the transverse and vertical planes was similar to that observed in the AD samples. These phases are mainly composed of Laves phase and carbides. However, the needle-like carbide phase was dispersedly precipitated within the grains and at grain boundaries, and exhibited full recrystallization and reduced dislocation density after SDA heat treatment. Consequently, the SDA samples presented superior strength-ductility balance to those of the AD and DA samples with irregularly shaped Laves phase and carbides owing to microstructural changes. For instance, the SDA heat treatment improved the ultimate tensile strength and fracture elongation of the vertical samples by up to 10.9% and 30.7%, respectively, whereas the microhardness decreased by 13.3% compared to the AD samples. The compressive residual stress of 98 MPa and tensile residual stress of 147 MPa were also observed on the surfaces of the SDA and AD samples, respectively. In addition, the SDA samples exhibited an almost isotropic tensile behavior in the vertical and horizontal directions as the epitaxially grown columnar grains transforms into equiaxed grains, as well as exhibited a prominent overall crystallographic texture. The effect of DA and SDA heat treatments on the mechanical properties were analyzed on the basis of stress–strain curves, hardening behavior, and multiple strengthening mechanisms.

High-temperature failure and microstructural investigation of wire-arc additive manufactured Rene 41

In developing a wire-arc plasma direct energy deposition process for creep-resistant alloys used in high-speed flight applications, structures were built from nickel-based superalloy Rene 41. Samples of additive manufacturing (AM) material were analysed for their microstructural and mechanical properties, in both as-deposited (AD) and heat-treated (HT) conditions. Tensile specimens were tested at room temperature, 538, 760, and 1000 °C. Macroscopically, large columnar grains made up of a typical dendritic structure were observed. Microscopically, significant segregation of heavier elements, grain boundary precipitates, and secondary phases were observed, with key differences observed in HT material. There was a clear distinction between failure modes at different testing temperatures and between AD and HT variants. A fractographic investigation found a progressive move from brittle to ductile fracture with increasing testing temperature in both AD and HT conditions, as well as microstructural features which support this observation.

Reducing directionally arranged substructure induced anisotropic mechanical properties of Hastelloy X superalloy fabricated by laser directed energy deposition

In this study, the effects of solution treatment (ST) on the microstructure and anisotropic mechanical properties of Hastelloy X fabricated by laser directed energy deposition (L-DED) were investigated. The microstructure of the as-deposited (AD) sample presented coarse granular grains aligned with the deposition direction. Due to the segregation of Mo and Cr elements, a special cellular-structure was formed in the inter-dendritic region, along with the strip-like carbides consisting of both M23C6 and M6C carbides. The cellular-structure homogenized rapidly after the ST. In detail, as the ST temperature increased, recrystallization generally occurred. Meanwhile, the strip carbides began to gradually dissolve and dissociate into dispersed particles which led to a drop in microhardness from 220 HV to 161 HV. The room temperature tensile results showed that the yield strength in the transversal direction (TD) and longitudinal direction (LD) decreased with the increase of ST temperature, reaching a minimum value of 285 MPa after the ST at 1175 °C. In addition, the ultimate tensile strength of the LD and TD samples reached maximum values of 693 MPa and 703 MPa at 1150 °C, respectively. It should be noted that the elongation of the low ductile TD sample can be improved significantly from 30% to 75% after the ST at 1175 °C. Therefore, it can be concluded that the anisotropy within the TD and LD samples can be effectively eliminated by controlling the cellular-structure, grain-structure, and carbide morphology during ST.

Effect of Post-Deposition Thermal Treatments on Tensile Properties of Cold Sprayed Ti6Al4V

This study aims at investigating the effect of various post-deposition thermal treatments on improving tensile properties of cold spray (CS) deposited titanium alloy Ti6Al4V. Dogbone-shaped tensile specimens were designed considering two application scenarios: ‘fully CS’ specimens, and ‘CS repair’ specimens. For both specimen types, tests were carried out in four conditions: (i) as-deposited (AD), and after three different thermal treatments, i.e., (ii) solution treatment and ageing (STA), (iii) hot isostatic pressing (HIP), and (iv) HIP followed by STA (HIP + STA). Complementary to tensile testing, characterisation of CS deposited material was also carried out in terms of microstructure and hardness. The STA process resulted in the highest improvement in ultimate tensile strength by more than 200%, reaching 868 MPa for ‘fully CS’ and 951 MPa for ‘CS repair’ specimens. However, no appreciable improvement in elongation at failure was achieved, highest being 1.2% for ‘fully CS’ after STA, and 4.3% for ‘CS repair’ after HIP. In addition to experimental investigation, a comprehensive collection of data from the open literature on the effect of various thermal treatments on improving the tensile properties of CS Ti6Al4V deposits is reported and discussed.

Microstructure-gradient approach for effective determination of post-heat treatment temperature of an additive manufactured Ti-6Al-4V sample

In this paper, a Ti-6Al-4V wall was fabricated using wire and arc additive manufacturing to be as-deposited (AD) coupons for investigating the effect of post-heat treatments on microstructure and mechanical properties. A Gleeble thermal-mechanical simulator was used to create a microstructure gradient in the sample with different heat treatment temperatures to efficiently determine the optimal post-treatment temperature, which is followed by furnace heat treatments to find proper aging (Age) conditions. Solid solution at 830 ℃ for 2 h followed by water cooling + aging at 500 ℃ for 4 h followed by furnace cooling was considered to be the optimal post-heat treatment candidate because it gained a 12.85% improvement of yield strength (YS) and 3.33% improvement of the ultimate tensile strength (UTS), though tensile fracture elongation (EL) decreased 3.37% compared to the as-deposited samples. With this condition, microstructure evolution including β grains, α widmanstätten, grain boundary α (GB α), and α’ martensite was characterized at the same position of the sample experienced deposition (AD), solid-solution treatment (AD-ST), and aging (AD-ST-Age) respectively. The relationship between such step-by-step microstructure evolution with tensile strength as well as hardness change was analyzed and established. In the end, brittle fracture surfaces of AD, AD-ST, and AD-ST-Age samples were observed to find the factors that contribute to failure.

Effect of heat treatment on the microstructure and tensile properties of a new superalloy designed for additive manufacturing

The microstructures and tensile properties of a novel superalloy especially designed for additive manufacturing (AM) were investigated under four states: (1) AD (as-deposited), the state of part after LMD (laser metal deposition); (2) HT1, heat treated at 870 °C for 16 h + air cooling; (3) HT2, heat treated at 1080 °C for 4 h + air cooling; (4) HT3, heat treated at 1080 °C for 4 h + air cooling, then heat treated at 870 °C for 16 h + air cooling (HT2+HT1). Each of them were extracted from the vertical (V) and horizontal (H) section of the part, respectively. Methods such as OM, SEM, TEM, XRD and unidirectional tensile tests were used for the investigation. The AD sample displays cellular dendrite microstructures with <001> crystal direction parallel to the building direction. The major phases are γ/γ'; while the minor phases are fine MC and Laves with no more than 1% in volume fraction. The size of primary γ′ ranges from 100 nm to 150 nm, the secondary γ′ particles are no more than 30 nm. With the aid of calculation, the processing HT1 and HT2 are confirmed as ageing and sub-solution treatment, respectively. The former raised the volume fraction of γ′ from 30.93% (AD) to 48.57% (HT1), and raised the size of γ′ at the expense of dissolving the secondary γ′ particles. The latter didn't change the volume fraction of γ′ strikingly, but refined the γ′ with the exception of a small amount of extraordinary large particles in the interdendritic region (IR). HT3 is a two-stage processing (HT2+HT1) which increased the volume fraction of γ′ slightly but raised the size apparently. The value of ultimate tensile strength (UTS) and yield strength (YS) of vertical samples are superior to that of the horizontal. The HT1-V shows the best UTS and poor Elongation (UTS, 1082 MPa; EL, 35.28%), while the AD-V has excellent strength and ductility match (UTS, 1054 MPa; YS, 744 MPa; EL, 50.45%); The best ductility is found among samples of HT3 (EL, 62.1% for HT3-H). The samples of HT2-H are inferior in both strength and ductility, and the obtained properties are scattered. These investigation results provide important fundamental support for optimizing the procedure, microstructure and properties of the new alloy in the future application research.

Effect of heat treatment patterns on porosity, microstructure, and mechanical properties of selective laser melted TiB2/Al–Si–Mg composite

Selective laser melted (SLM-ed) pre-alloyed TiB2/Al–Si–Mg composite reports tremendous engineering application potential. However, systematic research on its heat treatment (HT) patterns is scarce. This paper utilizes direct aging (DA), annealing treatment (AT), and solution-aging treatment (SAT) to investigate porosity, microstructure, and mechanical properties. The porosities of as-deposited (AD), DA, and AT samples remained at <1.1%, while the nanopores at the molten pool boundary of AD sample expanded into the molten pool inner of DA and AT samples. For the condition SAT, the porosity exceeded 4.8% accompanied by large-sized micropores. Porosity development resulted from the entrapped hydrogen diffusion along the eutectic Si interface. The HT had little effect on the TiB2 particles and near-equiaxed grains. The eutectic networks of AD and DA samples broke into separate particles after the AT and transformed into coarser particles in the SAT sample. The nanoscale (Si + β′′) and β′ precipitates were exhibited for the DA and SAT samples, respectively, while there are also a few composite precipitates. The evolution of eutectic and precipitates was related to the diffusion of supersaturated solutes. Due to the significant contribution of Orowan strengthening (∼213.1 MPa), a superior combination of the ultimate tensile strength (∼521.6 MPa) and yield strength (∼389.9 MPa) was realized after the DA. The excellent elongation (∼19.3%) of AT sample was attributed to the eutectic spheroidization. However, the high porosity of SAT sample severely compromised mechanical properties. This work provides essential guidance for HT selection of SLM-ed particle-reinforced Al–Si–Mg composites.

Microstructure and mechanical properties of wire arc additively manufactured 205A high strength aluminum alloy: The comparison of as-deposited and T6 heat-treated samples

In this study, the microstructure and mechanical properties of wire arc additive manufactured 205A high strength aluminum alloy were investigated. The samples in both the as-deposited (AD) condition and the T6 heat-treated (T6) condition were compared. The formed heterogeneous nucleation particles such as Al 3 Zr and Al 3 Ti promoted the formation of fine equiaxed grains with a low heat input. Some eutectics were dissolved during the solid solution process, with the appearance of secondary pores. A part of Cd was observed at the edge of the needle-like θ' phase, by transmission electron microscopy (TEM). In the subsequent aging process, the Cd atoms, vacancies, and Cu atoms formed Cu-Cd-vacancy clusters with lower activation energy than Cu atoms. Hence, the precipitation of the θ' phase was further promoted, which significantly improved the mechanical properties. The ultimate tensile strengths in the horizontal and vertical directions appeared isotropic and reached 510.2 MPa and 510.6 MPa, respectively. However, the eutectics and aggregated pores in the inter-layer regions resulted in the anisotropy of elongation. • The microstructure which mainly composed of equiaxed grains was obtained. • The heterogeneous nucleation cores were provided by Al 3 Zr and Al 3 Ti. • The mechanism of Cd promoting θ″ phases' precipitation was revealed. • The ultimate tensile strength reached 510.2 MPa after heat treatment. • The fracture mechanisms of 205A before and after heat treatment were analyzed.

Effect of deposit thickness on microstructure and mechanical properties at ambient and elevated temperatures for Inconel 718 superalloy fabricated by directed energy deposition

The effect of deposit thickness on the microstructure and the mechanical properties of Inconel 718 (IN718) fabricated by directed energy deposition was systematically investigated in both as-deposited (AD) and homogenization + solution + aging (HSA) treated conditions. Results indicate that deposit thickness for thin parts has a more significant impact on the microstructure and subsequent room (RT) and elevated temperature (650 °C) tensile properties compared to thick parts. Applying HSA treatment can effectively homogenize the microstructure of thick builds with a microstructure transition from columnar-dendritic grain structure presented in the AD condition to recrystallized equiaxted grain structure, which results in almost similar yield strength, ultimate tensile strength and ductility of ~ 970 MPa, ~ 1237 MPa, ~ 20% at RT and ~ 816 MPa, ~ 954 MPa, ~ 12% at 650 °C, respectively. In contrast, thin parts maintaining columnar grain features during HSA treatment yield a higher yield strength of 1112 MPa (increased by 15%) at RT and 936 MPa (increased by 15%) at 650 °C, but much lower ductility of 9% (decreased by 54%) at RT and 6% MPa (decreased by 51%) at 650 °C. The remaining large amount of residual stress primarily contribute to the enhancement of yield strength, as well as large amount of δ phase responsible for the much worse ductility for thin parts after HSA treatment. In addition, the underlying thermal history evolution in various deposit thickness is elucidated by the thermal simulations with the use of Finite Element Method (FEM) method within 3DExperience software. The results present in the current study show the capability of the directed energy deposition process to manufacture homogeneous components with varying thickness for high temperature application after a proper heat treatment, with regard to their initial as-deposited materials.

Wire laser metal deposition of 22% Cr duplex stainless steel: as-deposited and heat-treated microstructure and mechanical properties

Duplex stainless steel (DSS) blocks with dimensions of 150 × 70x30 mm3 were fabricated by Laser Metal Deposition with Wire (LMDw). Implementation of a programmable logic control system and the hot-wire technology provided a stable and consistent process producing high-quality and virtually defect-free deposits. Microstructure and mechanical properties were studied for as-deposited (AD) material and when heat-treated (HT) for 1 h at 1100 °C. The AD microstructure was inhomogeneous with highly ferritic areas with nitrides and austenitic regions with fine secondary austenite occurring in a periodic manner. Heat treatment produced a homogenized microstructure, free from nitrides and fine secondary austenite, with balanced ferrite and austenite fractions. Although some nitrogen was lost during LMDw, heat treatment or reheating by subsequent passes in AD allowed the formation of about 50% austenite. Mechanical properties fulfilled common requirements on strength and toughness in both as-deposited and heat-treated conditions achieving the highest strength in AD condition and best toughness and ductility in HT condition. Epitaxial ferrite growth, giving elongated grains along the build direction, resulted in somewhat higher toughness in both AD and HT conditions when cracks propagated perpendicular to the build direction. It was concluded that high-quality components can be produced by LMDw and that deposits can be used in either AD or HT conditions. The findings of this research provide valuable input for the fabrication of high-performance DSS AM components.Graphical

A comprehensive study of the anisotropic tensile properties of laser additive manufactured Ni-based superalloy after heat treatment

In this work, the anisotropic tensile properties of laser additive manufactured (LAMed) GH4169 in as deposited and different heat-treated conditions are presented and the underlying mechanisms are analyzed in detail. Vertical and horizontal specimens for tensile tests were taken from as deposited (AD) and heat-treated blocks. Two heat treatment conditions with solution temperature of 980 °C and 1050 °C were considered. The tensile test results indicate different tensile properties of the vertical and horizontal samples, and such anisotropy is related to heat treatment conditions. The vertical AD sample has higher tensile strength than its horizontal counterpart, while after heat treatment, the horizontal direction shows higher tensile strength. Microstructure characterization, texture and grain morphology analyses were conducted through SEM with EBSD, XRD and TEM observations in order to figure out the main influential factors of the anisotropic tensile properties. Besides, fracture surfaces of the tensile specimens were observed to study the role of precipitates. In addition, the residual stresses in the LAMed samples in AD and heat-treated conditions were measured, and their effects on the anisotropic tensile strength were clarified by correlating the residual stress levels with the recrystallization fractions extracted from EBSD data. The obtained results show that a large number of brittle Laves phases growing along the vertical direction are distributed in the AD samples, which leads to different separation manners of Laves phase/γ matrix interfaces under different loading directions. Besides, the residuals stress level is high direction dependent in the AD samples. After heat treatment, most of the Laves phases are dissolved, and the residual stress experiences a significant variation. On the whole, the anisotropic tensile strength is mainly influenced by the residual stress level before and after heat treatment, and slightly influenced by the dissolution of the Laves phase. The present study provides a deeper understanding of the anisotropic tensile properties of LAMed GH4169, which may contribute to future engineering applications of Ni-based superalloys.

Melt-quenched and as-deposited structures of amorphous selenium: a density functional/ molecular dynamics comparison

Molecular dynamics simulations using a density functional description of energies and forces have been carried out for a model of an as-deposited (AD) surface of amorphous selenium. The deposition model assumed the annealing (at 400 K) of layers of randomly located single atoms, followed by compression to the density used in earlier melt-quenched (MQ) simulations of amorphous Se, and by further annealing. The AD and MQ structures are predominantly twofold coordinated and similar, for example in the pair distribution functions, with notable differences: the AD structures have more defects (atoms with one and three neighbours), and the ring distributions differ. These differences are also reflected in the electronic structures of the AD and MQ samples, where the increased presence of defects in the former influences the Bader charges and the edge states of the band gap. The dominance of rings found in a previous simulation of AD structures is not found.

Friction and wear behaviour of BN(h) and Ag incorporated nickel phosphorous coatings under dry reciprocating sliding conditions

ABSTRACT Ni–P–BN(h)–Ag hybrid composite coatings were fabricated on the steel substrate by a scalable electroless deposition process. The optimum bath composition and operating conditions were selected to obtain defect-free composite coatings with ∼50 μm thickness. Further, to enhance the hardness, as-deposited coatings were subjected to heat treatment in a tubular furnace at 400°C for 1 h. The dry sliding wear behaviour of the as-deposited (AD) and heat-treated (HT400) composite coatings was evaluated using a linear reciprocating tribometer. The average friction coefficient of the hybrid coating was ∼0.14 (in as-deposited condition) and ∼0.16 (in heat-treated condition); these values represent 51.72% and 52.94% reduction over non-hybrid Ni-P coatings. The specific wear rate of the as-deposited and heattreated composite coatings was found to be 50% and 43% lower, respectively, than that of conventional Ni–P coatings. Detailed wear track analysis was carried out to identify underlying wear mechanisms and tribochemical interactions.

Effect of solution temperature on the microstructure and mechanical properties of Hastelloy X superalloy fabricated by laser directed energy deposition

In this study, the effect of solution temperature on the microstructure and mechanical properties of Hastelloy X fabricated by laser directed energy deposition (LDED) was investigated. As a result, the microstructure of as-deposited (AD) sample was mainly coarse columnar grains directionally growing along the deposition direction. Due to the segregation of Mo and Cr, a lot of Laves phase precipitates in the inter-dendritic. With the increase of solution temperature, the volume fraction of Laves phase gradually decreases. When the solution temperature increased to 1200 °C, the grains of the LDED Hastelloy X superalloy exhibited fully recrystallization, and then became coarse with the solution temperature of 1225 °C. With the dissolution of the Laves phase, the microhardness of the samples drops from 231 ± 5 HV to 211 ± 5 HV. The room temperature tensile results reveal that the as-deposited sample with irregular and long-striped Laves phase presents the worst tensile strength (652 ± 10 MPa) and elongation (30 ± 2%). After heat treatment, the strength and elongation of the LDED Hastelloy X superalloy gradually increased with increasing the solution temperature. When the solution temperature was 1200 °C, the tensile strength of the sample reached the maximum value of 720 ± 1 MPa. With the increase of solution temperature, the elongation increased and then reached the maximum value of 47 ± 2% with heat-treated at 1225 °C. The tensile fracture of LDED Hastelloy X superalloy with solution treatment presented a ductile fracture pattern.

Additively manufactured δ-ferrite-free 410 stainless steel with desirable performance

The 410 stainless steel (SS410) large-size block part without defects was successfully prepared by cold metal transfer (CMT) wire-arc additive manufacturing (WAAM). Results showed that δ-ferrite in SS410 could be eliminated during deposition without any extra post-treatment. The content of martensite in the central zone and overlap zone both exceeded 96%, and the rest was punctate austenite. The average strength/elongation of the as-deposited (AD) block part was 1323 MPa/4.1%. By comparing the tensile properties of AD samples with low-temperature annealing (LA), full annealing (FA), and high-temperature tempering (HT) post-heat-treated samples, the HT could achieve the best balance of strength and ductility with an elongation about 12.7%. This work proved that the high-performance parts could be prepared through WAAM by using appropriate processing parameters.

Effects of bath composition and thermal treatment on the performance of Co-Ni-Mo-P electrocatalyst supported on carbon for the electro-oxidation of ethanol

We explored the influence of bath compositions on the performance of as-deposited (ASD) Co-Ni-Mo-P electrocatalyst for the electrooxidation of ethanol using single-factor analysis. Further the effects of annealing temperature of the ASD electrocatalysts and influence of phosphorus on the catalyst performance were also evaluated. The specific peak currents for the forward (if) and backward (ib) oxidations and their ratios (if /ib) obtained from cyclic voltammetry (CV) were used to investigate and characterize the electrocatalyst performance. The results from the single-factor experiments showed that both current densities (if and ib) increased with increasing electroless bath concentrations for all the bath species studied. Using if /ib ratio as the response factor, an optimum bath molar ratio of NiSO4 (N): CoSO4 (C): Na2MoO4 (M): NaPH2O2 (P) for the as-deposited catalyst was identified as 13.0:100.0: 1.0: 94.0 which was equivalent to Ni:Co:Mo:P surface composition ratio of 3: 1.5: 1.0: 1.1 (Ni3Co1.5MoP1.1) in the electrocatalyst. The absence of phosphorus in the ASD electrocatalyst resulted in poor ethanol oxidation performance (low if /ib ratio) and low catalyst stability. An optimal temperature of 350 °C was determined for thermally treated ASD electrocatalyst under H2/Ar gas for which if and if /ib ratios were higher than at any other annealing temperature including the ASD electrocatalyst and this was attributed to the formation of a new phase - Co2Mo3. The stability of the thermally treated electrocatalyst was found to be lower than that of ASD electrocatalyst. Overall, the work provided a direction on the use of electroless deposition method to optimize and prepare electrocatalyst containing phosphorus for effective electrooxidation of ethanol.

Electrodeposition of ternary compounds for novel PV application and optimisation of electrodeposited CdMnTe thin-films

Growth of polycrystalline CdMnTe ternary compound thin films has been carried out using cathodic electrodeposition technique at different cathodic potentials. The range of the cathodic potentials used in this work has been chosen according to the cyclic voltammogram results. The CdMnTe thin films were electroplated from electrolyte containing CdSO4, TeO2 and MnSO4 in an acidic aqueous medium. Glass/fluorine-doped tin oxide (FTO) substrates have been used to electrodeposit the semiconductor layers. The structural, compositional, morphological, optical and electrical properties of the CdMnTe thin films were studied using X-ray diffraction (XRD), Sputtered neutral-mass spectroscopy (SNMS), Scanning electron microscopy (SEM), UV–Vis spectroscopy and Photo-electro-chemical (PEC) cell measurements respectively. The primarily grown as-deposited (AD) layers went through two different post-growth surface treatment conditions- heat-treated in air in the presence of CdCl2 (CCT) and heat-treated in air in the presence of GaCl3 (GCT). Results from the XRD indicated the polycrystalline nature of the electrodeposited films. The electroplated films have cubic crystal structures and the preferred orientation was found to be along the (111) plane of CdMnTe. Inclusion of Mn has been qualitatively observed using SNMS measurement. The optical energy bandgaps of the thin films were found to be varying between ~ 1.90 and ~ 2.20 eV. Though all the layers after post-treatment showed p-type electrical conduction, both p and n-type conductivity were obtained at different cathodic potentials for as-deposited materials. Comparison of the deposited layers to other electrodeposited ternary compounds has also been discussed.

Development of CdMnTe thin films using electroplating technique for opto-electronic device applications

Cathodic electrodeposition technique has been successfully used to achieve the growth of polycrystalline CdMnTe ternary compound thin films at different cathodic potentials. The choice of various cathodic potentials used in this work was made from the cyclic voltammogram results. The CdMnTe thin films were electroplated from electrolytes containing CdSO4, TeO2 and MnSO4·H2O in an acidic aqueous medium. The electrodeposition was carried out on glass/fluorine-doped tin oxide {FTO} substrates. The structural, optical, morphological and electrical properties of the CdMnTe thin films were studied using X-ray diffraction (XRD), UV–Vis spectroscopy, scanning electron microscopy (SEM), current–voltage (I–V) characteristics and photo-electro-chemical (PEC) cell measurements respectively. The materials investigated in this work were explored under three different conditions namely: as-deposited (AD), heat-treated ordinarily in air (HT) and heat-treated in air in the presence of CdCl2 surface treatment (CC). Results from the XRD showed that the electrodeposited films are polycrystalline with the presence of CdTexOy and CdMnTe peaks. The electroplated films have cubic crystal structures and the preferred orientation was found to be along the (111) plane. The optical energy bandgaps of the thin films were found to be deposition potential dependent. Electrical conductivity types namely p- and n-type conductivity were also obtained at different cathodic potentials using photo-electro-chemical cell measurement technique for as-deposited and heat-treated materials.