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When polyoxymethylene (POM)—a common polymer used in metal injection moulding feedstock—is exposed to heat and oxygen during compounding, it can be easily decomposed, releasing undesired gaseous formaldehyde products. In order to reduce the formaldehyde emission from POM, amine treatment was performed. The effectiveness of propylamine at different concentrations and its role as a formaldehyde scavenger was studied via the UV–vis Spectrophotometry, Fourier Transform Infra-red, Thermogravimetric Analysis, Scanning Electron Microscopy, and melt flow index. The results proved that a simple amine, such as propylamine, is a promising candidate for scavenging formaldehyde in POM. It is also demonstrated that the best concentration of propylamine is 2 wt.% (POM-PA2) with a minimum formaldehyde emission of 1.44 mg/L. Further, when used in formulating metal injection moulding feedstock (MIM), the POM-PA2 reveals good rheological properties and high green strength. These advantages make the modified polyoxymethylene (POM-PA2) a promising binder system for MIM feedstock.

Titanium possesses excellent mechanical properties, unrivalled corrosion resistance, and biocompatibility. Still, it is restricted to some niche applications due to its high embodied energy consumption and production cost. The Kroll process used for most commercial titanium powder production is energy-intensive, non-eco-friendly, and costly. The increased production cost and environmental issues have resulted in enormous research and development activities to develop new methods to produce high-purity titanium powder economically and eco-friendly. These new methods have been categorised into three primary groups: thermochemical, electrochemical, and solution-phase methods. Recent developments are focused on the electrolysis process, including cathodic and anodic reduction. Recent development in hydrogen-assisted magnesiothermic reduction (HAMR) seems promising to produce high-purity titanium at a low cost and low energy consumption. This article, for the first time, discusses the solution-phase methods to produce titanium powder directly. Particular emphasis on the sustainable production of titanium has also been highlighted.

The use of polyethylene glycol (PEG) and poly methylmethacrylate (PMMA) as a binder for metal injection moulding (MIM) operation results in void formation in the MIM feedstock. In order to formulate a practicable PEG/PMMA binder system, we identified a crystallisation inhibitor - polyvinyl acetate (PVAc) – to suppress the void formation. Rheological behaviour of the feedstocks with varying amounts of PVAc was compared with a previously reported feedstock based on the crystallisation inhibitor polyvinypyrrolidone (PVP). The analysis of rheology tests reveals that the incorporation of PVAc into PEG/PMMA binder system does not affect the overall rheology of the feedstocks. Differential scanning calorimetry (DSC), thermal gravimetric analysis (TGA) and microstructural analysis along with impurity measurement of the sintered samples were carried out for complete evaluation. The DSC analysis suggests interactions between components of the binder system. These interactions were further verified using Fourier-transform infrared spectroscopy (FTIR), which reveals possible complex hydrogen bonding interactions in the ternary blend systems. Overall, the results show that the addition of PVAc into the PEG/PMMA binder system produces Ti-MIM feedstocks with good rheological properties resulting in void-free injection moulded samples, and acceptable mechanical properties (tensile strength ~550 MPa; elongation ~10%).

Superhydrophobic surfaces – driven from natural biology – are being increasingly studied in many engineering fields. This study fabricated hydrophobic AAO/Ni coatings and superhydrophobic AAO/Ni/Ni...

A series of Co–P–TiO2 nanocomposite coatings were prepared via pulsed electrodeposition technique. TiO2 nanoparticles were embedded into the coating matrix using TiO2 sol. The phase constituents of...

Chromium coatings are largely restricted in electrical and electronic industries due to the environmental concerns. To address these concerns, a cobalt–phosphorus–titanium oxide (Co–P–TiO2) nanocomposite coating is developed in this study using a nanoparticle-reinforced electrodeposition process. The effects of TiO2 nanoparticles on the properties of co-deposited Co–P–TiO2 nanocomposite coatings are investigated. The surface characterisation is carried out by scanning electron microscopy and atomic force microscopy, while the crystal structure is studied using X-ray diffraction. The mechanical properties of nanocomposite coatings including microhardness and wear resistance are also determined. To study the electrochemical behaviour of the coatings, the potentiodynamic polarisation analysis combined with electrochemical impedance spectroscopy is performed. The Co–P–TiO2 coating at 1 g/L TiO2 addition displays the best physicochemical performance. Compared to Co–P coating, the mechanical properties of the nanocomposite coating are significantly improved by the strengthening effects of the well-dispersed TiO2 particles. Excellent corrosion resistance is also achieved for the Co–P–TiO2 at proper TiO2 addition due to its smooth and defect-free microstructure. However, it is found that the excessive addition of TiO2 decreases the coating quality, resulting in an unfavourable microstructure and properties.

During spark plasma sintering (SPS), the gas atomized powders experience a sequence of densification mechanisms of particle arrangement, viscous flow, and high temperature creep concurrent with grain growth. However, after short time ball-milling of the original powders, the dramatic change of powder shape affects the thermodynamics (densification mechanisms) and kinetics (mass transfer) of powder densification based on the evolution of characteristic microstructure and densification data. In addition, we establish a theoretical framework to determine an atomic diffusivity DT, by incorporating the contribution of the applied pressure to the densification kinetics. Furthermore, the DT can be utilized to govern powder densification during SPS. Accordingly, a larger DT associated with the irregular metallic glass powder gives rise to faster powder densification, as compared with the original spherical powder without mechanical milling.

A newly developed porous Ti35Zr28Nb scaffold was manufactured via powder metallurgy (PM) using space-holder (NH4HCO3) sintering from pre-alloyed powder. The pore features, compression and anti-corrosion properties of the manufactured porous scaffolds were systematically studied. The results show that all the manufactured porous Ti35Zr28Nb scaffolds consisted of a single β phase. The porosity of the porous Ti35Zr28Nb scaffolds increased from 50% to 65% with in increasing the NH4HCO3 from 63% to 79% (volume ratio), and the average pore size (d50) was in the range of 230–430 μm. The yield strength in compression and the elastic modulus of the porous Ti35Zr28Nb scaffolds both decreased gradually with an increase in porosity, varying from 230.5 MPa to 79.7 MPa and 6.9 GPa to 1.8 GPa, respectively. The corrosion rate of the porous Ti35Zr28Nb scaffolds in the phosphate buffer saline (PBS) solution increased from 0.91 × 10−3 mm/yr to 4.18 × 10−3 mm/yr with an increase in porosity from 51.4% to 64.9%. In comparison with unalloyed Ti scaffolds with almost the same porosity, the porous Ti35Zr28Nb scaffolds showed a significantly higher compressive yield strength and a lower corrosion rate. These results suggest that porous Ti35Zr28Nb scaffolds fabricated by PM have substantial potential for hard-tissue engineering applications. Additionally, the relationship of porosity, mechanical and anti-corrosion properties of these Ti35Zr28Nb scaffolds has now been confirmed, and could be used in the process of material selection for their specific applications. Keywords: Corrosion resistance, Mechanical property, Porous Ti35Zr28Nb scaffold, Powder metallurgy, Pore characterization

This study determined the optimal concentration of titanium diboride (TiB2) particles for the development of in situ titanium–titanium boride (Ti–TiB) metal matrix composites (MMCs) prepared by a conventional powder metallurgy route to be used for industrial applications. The effect of concentration of TiB2 particles was studied by reinforcing TiB2 powder in different mass fractions (2wt%, 5wt%, 10wt%, and 20wt%) into pure Ti powder during the fabrication process. The MMCs were sintered at high temperatures under vacuum. The transmission electron microscopy (TEM) results revealed the formation of needle-shaped TiB whiskers, indicating that in situ reaction occurred during vacuum sintering of the powder compacts. All the composite samples had a high sintered density, and the hardness of the composites increased with an increase in the mass fraction of reinforcement. Mechanical and tribological properties such as flexural strength, impact, and wear properties were determined and found to be dependent on the mass fraction of the reinforcement. However, the mechanism for the in situ reaction needs further investigation by high-energy in situ X-ray diffraction techniques.

Titanium matrix composites (TMCs) offer high specific strength and stiffness compared with steel and nickel-base materials. High-temperature TMCs can offer up to 50% weight reduction relative to monolithic superalloys while maintaining equivalent strength and stiffness in jet engine propulsion systems. Regardless of the reinforcements are continuous fibres or discontinuous particulates, the unique properties of TMCs have thrust them to the forefront of extensive research and development programmes around the world. Even though TMCs are one of the most studied and sought-after material systems, useful information about their properties, fabrication methods and design is scattered in the literature. This review covers important research work that has led to the advances in TMCs material systems. It also provides comprehensive details about common reinforcements, manufacturing processes, and reviews static and dynamic properties of some common TMCs. The review also presents common industrial applications of TMCs and highlights the promising outlook of TMCs.

The use of silicon nitride (Si3N4) particles as potential reinforcement for titanium metal matrix composites (Ti-MMCs) was evaluated. Si3N4/Ti composite samples were fabricated by a conventional press and sinter route. The effects of sintering temperature and the concentration of Si3N4 in Ti matrix were investigated with respect to phase constituents, microstructure and tribology properties. Si3N4 weight fraction inside the Ti matrix was found to be the key parameter determining phase constituents and overall properties even at lower concentrations. Because of its instability in Ti at higher temperatures, in situ reactions between the reinforcing particles and matrix led to the formation of phases such as Ti5Si3 and possibly Ti3Si, in the composites containing higher fractions of Si3N4. The formation of homogeneous Ti5Si3 phase resulted in excellent wear properties at the expense of ductility. The wear resistance was directly proportional to the weight fraction of Si3N4. The highest hardness value 949HV1 was recorded for Ti-5 wt% Si3N4 composite when sintered at 1300 °C for 3 h. This work will benefit in understanding these composites as a prospective wear resistant material in industrial applications.

Recent years have witnessed extensive investigations of additively manufactured NiTi alloys using laser-source techniques. This study reports a selective electron beam melting process to make Ni-rich NiTi parts using the plasma rotating electrode processed pre-alloyed NiTi powder. Microstructures of the as-printed NiTi samples were investigated, including micro-morphology, phase constituent and texture. Chemical compositions (primarily oxygen and nickel) and martensitic transformation temperatures were compared between the in house made NiTi powders and as-printed NiTi samples. X-ray diffraction results show that the as-printed samples exhibit a dominant austenitic B2 phase and a minor in situ formed Ni4Ti3 phase. The as-printed samples demonstrate a strong B2 (001) orientation texture along the building direction. Differential scanning calorimetry results show asymmetric phase transformations: a two-step of B2 → R → B19′ phase transformation during cooling but a one-step B19′ → B2 transformation during heating. Excellent superelasticity and large reversible strain have been observed. The as-printed NiTi samples achieve a fracture tensile stress of 1411.0 ± 59.3 MPa and an elongation of 11.8 ± 0.9%. The observed tension-compression asymmetry has been also discussed.

At present, the binder’s properties for metal injection molding (MIM) are assessed by rheological measurements and thermal decomposition temperature of the backbone polymer. Although blend studies of common polymers are available in the literature, little attention has been paid to study specific interactions among the particular binder system components and the effects of such interaction on reactive powders-MIM feedstocks are largely missing. This chapter aims to give readers some basic knowledge about polymer blends, their thermodynamics, and the possible interactions among individual components of common binder systems. In the last section, interactions between a binder system and metallic powder are also explained. After going through this chapter, the readers should be able to identify the importance of such interactions and know-how these interactions can be used to improve the properties of a feedstock.

In this study, corrosion, wear, and tribocorrosion of Ti-16Mo alloy manufactured by powder metallurgy (PM) in phosphate-buffered saline are investigated. The results indicate that the corrosion rate of Ti-16Mo alloy increases about 100 times from 0.00009 mm/yr to 0.00851 mm/yr under the tribocorrosion condition. Also, corrosion accelerates wear loss, and wear increment rate due to the corrosion (4.7715 mm/yr) of Ti-16Mo alloy is about 40% of pure mechanical wear rate (11.78 mm/yr). Compared with as-cast pure Ti (23.70999 mm/yr) and Ti-6Al-4 V (17.12003 mm/yr), Ti-16Mo alloy exhibits the lowest materials loss of 16.56001 mm/yr making it become a promising alloy for bone-tissue applications.

The control of impurities—mainly carbon, oxygen, hydrogen, and nitrogen—is a key aspect of metal injection molding (MIM). The two most critical impurity elements to consider for reactive powders are oxygen and carbon because titanium has a high affinity toward oxygen and all binders are essentially carbon-based chains. This chapter highlights the importance of impurity control and the impact of it on mechanical properties. It also discusses the processing steps that should be taken to keep it in check.

This chapter briefly introduces each step involved in metal injection molding. It also introduces the evolution of metal injection molding technologies, opportunities, applications, and some constraints.

The binder system is an integral part of the metal injection molding (MIM) process. This chapter presents a general classification of the binder systems used for reactive powders MIM and discusses the critical aspects in terms of feedstock chemistry and properties. The first section of the chapter focuses on the binders’ chemistry. The importance of the main constituent in binder systems is highlighted. Classification of the binder systems and their subsequent removal after the injection molding process are discussed in the next section. Feedstock chemistry and properties are discussed in the final section, with a focus on the critical aspects of feedstock technology such as effects of solids loading and shear sensitivity in detail.

This chapter provides information on some potential feedstocks used for metal injection molding of reactive metals. It also reports a few successful case studies of using either commercial or custom-made feedstocks.

This chapter provides perspectives of the future trends in reactive metallic powder injection molding.

This paper characterises and evaluates Si3N4/Ti composites during thermal treatment using an in situ neutron diffraction technique. The composites were developed using a conventional press and sinter technique. Pure titanium (Ti) was chosen as the matrix, and different concentrations of Si3N4 were used as the reinforcement. The effects of sintering temperature and the concentration of Si3N4 in the Ti matrix were investigated with respect to phase constituents. The Si3N4 weight fraction in the Ti matrix was found to be the key parameter for the reaction. Because of its instability in Ti at higher temperatures, in situ reactions between the reinforcing particles and matrix led to the formation of intermetallic compounds, such as Ti5Si3 and possibly Ti3Si, in the composites containing higher weight fractions of Si3N4. This work helps in understanding these composites as a prospective material in industrial applications.

It has been challenging to achieve good strength-ductility synergy in titanium metal matrix composites (Ti-MMCs). Herein we report a new Ti-MMC produced by multi-directional forging (MDF) undertaken in near β phase region. The developed composite exhibits a microstructure featuring dynamically recrystallized (DRX) ultrafine α-Ti matrix with uniformly dispersed micrometer sized TiB whiskers and submicrometer sized Y2O3 particles. This unique microstructure renders the composite an exceptionally high strength and good ductility at room temperature. The strengthening mechanism of the dually reinforced Ti composite is discussed.

This study investigated the sublimation of Mn and microstructural evolution of binary Fe/Mn compacts sintered at various temperatures in a vacuum. A high sintering temperature or a lengthy holding time promotes powder densification. Due to sublimation of Mn, the weight loss of the compacts mainly occurs during the isothermal holding stage of the sintering process; it increases significantly from 1.5 wt.% for sintering at 1000 °C to 8.6 wt.% at 1200 °C. For the first time, the phase evolution in the binary elemental compacts was clarified using in situ neutron diffraction. The γ-austenite phase emerges during temperature ramping to 536 °C, while β-Mn and α-Fe disappear at 774 °C and 881 °C. The neutron diffraction also revealed that single phase γ-austenite forms in the Fe-Mn compacts if the temperature is ≥ 881 °C.

Titanium alloys have been widely used for medical implants due to their good biocompatibility and excellent corrosion resistance. 60NiTi, an intermetallic nickel-titanium alloy containing approximately 60 wt.% Ni and 40 wt.% Ti, is a promising material for medical components such as implants and prostheses. 60NiTi is hard with good biocompatibility, highly corrosion resistant and has relatively low stiffness. In this study, conventional press-and -sinter method was employed to produce porous 60NiTi parts suitable for general bone replacement applications such as spinal and cranial inserts. The effect of solution treatment in a non-protected furnace and water quenching on the mechanical and microstructural properties of 60NiTi were investigated. It was found that this procedure produces a hard integral ceramic layer, a complex mixture of nickel and titanium oxide compounds, on the surface and around the pores of 60NiTi parts. Results showed that this heat treatment procedure causes the embrittlement of the parts due to an increase in oxide content. However, the produced ceramic surface can also enhance the resistance to corrosion, which is beneficial from a biocompatibility point of view.

Impurity control remains to be a challenge to titanium metal injection moulding (Ti-MIM). Much attention has been paid to polyethylene glycol (PEG) based binder systems due to the eco-friendly and water-soluble feature of PEG. In this study, a new easy-to-debind PEG/polypropylene carbonate (PPC)-based binder system (76% PEG+17% PPC+3% polymethyl methacrylate (PMMA)+2% stearic acid (SA)+2% polyvinyl acetate (PVAc)) was developed. The rheological properties of the feedstocks prepared with the binder system in different proportions were assessed. Debinding behaviours of the moulded samples and impurity contents of oxygen (O), carbon (C), and nitrogen (N) of the thermal debound specimens were investigated as well.

Binder system is an integral part of metal injection moulding (MIM) process that holds the metal powder together until the first stage of sintering. In this research, a new binder system was developed consisting of water soluble polyethylene glycol (PEG) as the main component, while poly (propylene carbonate) (PPC) and poly (methyl methacrylate) (PMMA) were used as the backbone components for titanium-MIM processing. The macromolecular interactions between various binder components were evident from Fourier-transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM) studies. The interactions between polymeric components in the binder provided ample compatibility within the binder system as revealed from the thermo-rheological properties of the titanium-MIM feedstock, which ensured suitability for thermal processing. Incorporation of PMMA in PEG/PPC binder system significantly improved the green strength of the moulded parts especially after initial water debinding step and thereby facilitated the following thermal processing. In addition, the chemical interactions between the polymers in PMMA-containing binder system enhanced the thermal stability of the as-moulded parts. Hence, the interactions between different polymeric materials showed a crucial role in developing suitable binder system for the MIM processing. The oxygen, carbon and nitrogen impurity contents of thermally debound samples obtained from this new binder system met the grade 1 ASTM standard, suggesting the potential applicability in the production of high quality titanium products.

Metal matrix composites (MMCs) are the new generation materials that combine both the metallic properties (ductility and toughness) and ceramic characteristics (high strength and modulus), leading to higher strength in shear and compression, at higher service temperatures. Titanium matrix composites possess light weight, high strength and good corrosion resistance and are used as structural materials in automobiles and aerospace industries. In the present study, in situ Ti-TiB composites were fabricated by reinforcing (2, 5, 10 and 20 wt. %) TiB2 powder (mean size

NiTi is characterized as a shape memory alloy that has found interesting applications from aerospace to biomedical engineering. The use of NiTi in biomedical applications is due to its excellent biocompatibility, shape memory and pseudoelastic properties. These properties make NiTi an excellent candidate for many functional designs in biomedical fields. However, difficulties in manufacturing and processing of this alloy are significant hindrance to widespread applications. Advances in additive manufacturing (AM) such as selective laser and electron beam techniques have provided opportunities in manufacturing complex shaped NiTi parts. In this research paper, we demonstrate manufacturing of NiTi parts using a selective electron beam melting (SEBM) technique. Complete evaluation of physical, chemical and mechanical properties was carried out to determine the suitability of SEBM process. Differential scanning calorimeter (DSC), X-ray diffraction (XRD), and metallographic analyses were employed for the thermal and structural characterizations. The obtained results suggest that it is imperative to, and challenging to control the additive manufacturing process in order to obtain the desired microstructures and avoid unwanted texture. An exhaustive heat treatment of the samples after SEBM process might also be necessary.

This work investigated the effects of current density and deposition time on the properties of electrodeposited PbO2. The PbO2 preparation was conducted on Ti/SnO2–Sb substrates by galvanostatic anodic deposition in a newly proposed methanesulfonate electrolytic solution. Phase constituents and microstructures of the deposited PbO2 coatings were characterized. Increasing current density in the range ≤ 100 mA cm− 2 leads to the formation of highly textured coatings with an increased content of α-PbO2 phase. Concurrently, a high current density favors a compact and flat surface morphology. The study of deposition time indicates a change of crystallite growth manner from an initially random growth to a later-stage preferred growth along distinct orientations. The change of crystallite growth is corroborated by the cross-sectional microstructures of the PbO2 deposits. The microstructural transition occurs only in the initial deposition stage. After a brief period, prolonged electrodeposition barely changes the surface morphology of PbO2 coatings.

In this work, PbO2 electrodes were prepared by pulse reverse current (PRC) electrodeposition. The effect of different duty cycles was investigated, which confirms that PRC deposition is an effective technique to optimize PbO2 electrodeposition. Surface morphologies and crystal structures of the PbO2 electrodes were characterized, and the voltammetric study was conducted to elucidate their electrochemical behavior. PRC deposition markedly changed the crystal structural and morphologic features of the resulting PbO2 electrodes, giving rise to the increased content of β phase and a rough surface morphology. High-performance liquid chromatography (HPLC) was employed to monitor the galvanostatic electrolysis of benzoic acid (BA) occurring over the PbO2 electrodes. A pseudo first-order reaction was found to well fit these BA degradation reactions, and the highest degradation efficiency was observed for the PbO2 electrode made from 95% duty cycle. Concurrently, main aromatic intermediates and carboxylic acids generated in the BA degradation were identified, and a probable pathway was proposed for the BA degradation course on the PbO2 anode.

Polyethylene glycol (PEG), with polymethyl methacrylate (PMMA) as the backbone binder component, is a common primary binder component in the design of water soluble binder systems for metal injection moulding (MIM). However, PEG crystallises upon cooling, producing voids in the injection moulded parts. These voids ultimately lead to porosity and degraded mechanical properties in the sintered bodies. We have previously reported on the use of polyvinylpyrrolidone (PVP) as a crystallisation inhibitor in the PEG/PMMA binder system to suppress void formation. In this paper, PEG/PMMA/PVP binder-based feedstocks were prepared with a 67 vol% solid loading in order to evaluate the effects of PVP incorporation on the PEG/PMMA binder for titanium MIM. The homogeneity and rheological behaviours of the feedstocks with varying amounts of PVP were compared with the base PEG/PMMA binder-based feedstock. Microstructural observation, impurity measurement and mechanical testing were carried out. It was found that incorporation of 20 wt% PVP into the PEG produced a void-free, high quality Ti-MIM component, with an average final density of 98% and a tensile elongation of 9.5%.

Titanium (Ti) based porous alloys have been widely used as orthopedic implants. However, the successful applications of these porous Ti alloys need to have the ability to mimic the mechanical properties of natural bone. Novel porous Ti35Zr28Nb scaffolds were fabricated via powder metallurgy (PM), and the fabricated scaffold with 61.1% porosity exhibited favorable mechanical properties with a compression yield strength of 132.5 ± 3.5 MPa and an elastic modulus of 2.9 ± 0.4 GPa, which are desired mechanical properties for bone implant material applications. The extracts of the porous Ti35Zr28Nb scaffolds showed no toxic effect on cell proliferation in vitro and their cytotoxicity grade was at level 0, similar to that of as-cast pure Ti and Ti-6Al-4 V alloy. Additionally, the extracellular alkaline phosphatase (ALP) level of MC3T3-E1 indicated that the bone matrix synthesis on the porous Ti35Zr28Nb scaffolds was slightly higher than that of as-cast Ti-6Al-4 V and pure Ti alloys. After implantation in rat distal femurs for 8 weeks, the porous Ti35Zr28Nb scaffolds were surrounded by new bone tissue, and the numbers of red blood cells, white blood cells, immunocyte cells, and neutrophil cells returned to the normal levels, which indicate that the porous Ti35Zr28Nb scaffolds possess good in vivo osteointegration ability and hemocompatibility. It hence can be concluded that the PM-fabricated Ti35Zr28Nb scaffolds, which have desired mechanical properties and excellent biocompatibility and osteointegration, are a promising candidate alloy for bone-tissue engineering applications in orthopedics.

Aluminum often requires protective coatings to prevent corrosion. The aluminum alloy substrate usually needs pretreatment to minimize, stabilize or convert the surface oxide in order to achieve adequate coating adhesion. The electrodeposited Ni-P coating is a promising candidate as a protective coating due to its easy fabrication and excellent performance. This study comprehensively investigates the pretreatment of zincating and anodizing on 6061 aluminum alloy, and systematically discusses their influence on the electrodeposited Ni-P coatings. The crystal structure and elemental composition were investigated for interlayers and Ni-P coatings subsequently, while morphologies of the coating surface and cross-section were also determined. The results revealed similar phase composition for differently pretreated Ni-P coatings, while distinct nodule featured morphology was observed for anodized Ni-P coating. It was found that anodized Ni-P coatings had the best performance due to its superior coating adhesion, wear-resistance, and corrosion resistance. In contrast, severe wear damage was occurred to zincated Ni-P coatings due to its inferior microstructure and weak zinc interlayer. Lastly, the influence of anodizing pretreatment on the coating microstructure is discussed, and a model is proposed for Ni-P electrodeposition employing anodizing pretreatment.

This study reported the preparation of homogeneous hydride–dehydride (HDH) titanium metal injection moulding (Ti-MIM) feedstocks using solvent mixing. The research emphasis was on the development of a binder system for producing higher solid loadings for the irregular HDH titanium powder feedstocks. Homogeneous mixing and solid loading are the factors that strongly influence the final product properties. Solvent mixing provides an excellent alternative to the commonly used hot mixing and emulsion mixing. Due to its natural irregular shape of HDH-Ti powder, the feedstock, which is injection mouldable, usually has a lower solid loading than that of spherical powder. In this study, Ti-MIM feedstocks were prepared using polyethylene glycol (PEG) as the primary binder component, polymethyl methacrylate (PMMA) as the backbone component and a new lubricant. The binder and metal powders were mixed in acetone and then vacuum dried. Scanning electron microscopic (SEM) analysis, rheometry tests and torque measurements were performed subsequently.

In this work, we prepared titanium matrix composites (TMCs) reinforced with in-situ polycarbosilane (PCS)-derived TiC particles. The effects of PCS addition on the microstructure, interface, hardness, and tribological properties were studied. The pyrolysis of PCS leads to the formation of in-situ TiC particles and Si solid-solution at a low PCS content (≤3 wt%). The TiC particles with a particle size of 4.8 μm are uniformly distributed in TMCs and have a well-bonded interface with the Ti matrix. The average grain size of α-Ti decreases from 100.5 μm in pure Ti to 16.1 μm in the Ti-3 wt% PCS composite. The presence of in situ synthesized TiC particles contributes to the excellent wear resistance of the Ti/PCS composites, which is ascribed to the increased hardness, superior load transfer capability, and oxidation wear resistance. The Ti-3 wt% PCS composite possesses the hardness of 4.72 GPa, elastic modulus of 169.23 GPa, and a low specific wear rate of 0.84 × 10−12 m3/(N·m) under constant conditions (3 N, 0.03 m/s). These values are all superior to those of Ti-6Al-4V alloy. This work sheds light on the design of high wear-resistant TMCs for industrial applications.

The field of particulate reinforced titanium matrix composites (TMCs) has seen significant progress and breakthroughs over the last two decades. Among the particulate reinforced TMCs, Ti/TiB composites have been studied and well adopted in the industry. Despite many advantages, Ti/TiB composites, however, do not possess high wear resistance. Contrary to Ti/TiB composites, incorporation of Si3N4 into the Ti matrix can significantly increase the wear resistance. This study makes use of both reinforcements (Ti/TiB composite as core material and Ti/Si3N4 as shell material) to produce a high strength, high wear-resistant hybrid composite system. The resultant composites were characterized using X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses. The results revealed complete decomposition of Si3N4 reinforcement and the formation of needle-shaped TiB whiskers, indicating that in situ reaction occurred during the vacuum sintering of the powder compacts. All the composite samples had a high sintered density. The hardness of the composites increased with an increase in the mass fraction of Si3N4. Tensile strength and tribological properties were determined and found to be dependent on the mass fraction of the reinforcements, respectively. The results show that by combining the two reinforcements, composite with a high-strength core and a high wear-resistant surface can be realized.