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UV protection and coatings for plastics are important in many applications. The cladding of low microwave (MW) absorption composite coatings on high MW transparent plastic substrates is a challenge due to their disparate dielectric properties. Moreover, an uneven heat energy conversion within the composite creates an additional hurdle in producing a coating with good surface integrity. In this study, a protocol was developed to overcome these difficulties based on a hybrid approach. The adverse effect of temperature mismatch between the coating and substrate was reduced through a two-way susceptor-aided heating mechanism. Low MW absorbing sol–gel derived composite coatings consisting of silicon dioxide (SiO2) and titanium dioxide (TiO2) were successfully cladded on the surface of MW and visual light transparent polycarbonate to produce a clear protective coating with UV-resistance. Nanoindentation tests were conducted to assess the effectiveness of the proposed protocol. Significant enhancement in the surface elastic modulus and hardness were achieved.

The present study proposes an efficient processing scheme for fabricating carbon nanotubes (CNTs)-reinforced magnesium (Mg) alloy AZ61 composite foams with enhanced compressive and energy absorption properties. The scheme combines powder metallurgy, rapid microwave (MW) sintering, and pore wall reinforcement to overcome the low strength, non-uniform pore structure, prolonged sintering process, and high production cost associated with conventional unreinforced Mg-based foams. In the proposed scheme, a dual-stage mixing method is used to homogeneously disperse and incorporate CNTs into the matrix for strength enhancement, and susceptor role, and carbamide granules are used to control the pore size and porosity fractions. In addition, MW sintering is used to rapidly consolidate the samples in 20 min through the synergy between an external and an internal susceptor (i.e. CNTs), which facilitates uniform and volumetric heating of the entire samples. Thus, sample oxidation and the formation of deleterious secondary phases are minimised, while up to 69% energy is saved. Experimental results show that the dispersion and incorporation of CNTs into the matrix, via the present processing scheme, clearly enhance the compressive and energy absorption properties of the composite foams, as compared with the unreinforced foams. The proposed processing scheme is a rapid and energy-saving efficient technique, which can be used to fabricate high quality Mg alloy composite foams with improved compression and energy absorption properties.

Microwave heating is an efficient alternative approach for synthetic chemistry with many distinctive advantages of high heating rate, selective and homogeneous heating. In this study, a new laser-microwave hybridization method, which comprises laser micropatterning, microwave heating and in situ synthesis has been developed to produce titania/hydroxyapatite/tricalcium phosphate (TiO 2 /HA/TCP) composite coating on titanium alloy (Ti6Al4V) substrate. The composite coating with a fine porous network microarchitecture was selectively produced on the Ti6Al4V surface by laser ablation and alkaline treatment. Using TiO 2 sol-gel and mixed powders of calcium carbonate (CaCO 3 ) and dicalcium phosphate dihydrate (CaHPO 4 ·2H 2 O), the composite coating synthesized at a temperature of 800 °C in a short time of 20 min exhibited homogeneous microstructure, strong hydrophilicity and good adhesion strength of 34 MPa. The in vitro apatite-forming capability of the coating was examined by immersing the coated Ti6Al4V specimen into a simulated body fluid (SBF) for up to 7 days. Biodissolution was observed in the early stage of incubation, followed by apatite precipitation. The quantity and size of the apatite globules increased over time. After 7 days of immersion, the coating surface was nearly covered by a layer of bone-like apatite, showing a significant improvement of its osteoconductive property over the uncoated sample. The laser-microwave hybridization provides an efficient route to synthesize HA/TCP based coatings for bioactivity enhancement, and serves as an effective sterilization tool for implant materials.

Finite element modelling of a magnesium alloy matrix filled with a 2% volume fraction of carbon nanotubes (CNT) under 2.45 GHz microwave (MW) irradiation is reported. The effective dielectric and permeability data of the simulated compact are evaluated using the effective medium approximation. Subsequently, these values are used to solve Maxwell’s electromagnetic equations followed by the heat conduction equation, thus both the field distribution in the oven cavity and the predicted heating of the model compact are obtained. At an applied power of 1 kW and a 9-minute simulation time, the results show poor coupling between the monolithic metal compact and the MW, resulting in a maximum temperature of ~163 °C. It is in good agreement with earlier studies and theory in which metals did not couple very well with MWs at room temperatures. The model also predicts the temperature in the 2% CNT-filled alloy compact to be 13 °C higher than in the monolithic compact after a similar simulated microwave irradiation duration. Furthermore, the effect of susceptor-assisted microwave heating is investigated by introducing a susceptor kiln into the model. Simulation results predict the temperature of the compact to rise to about 600 °C after 9 minutes, highlighting the importance of susceptor-assisted sintering. The model developed is significant in providing important details for predicting the response of metal compacts and their composites to MW heating as well as further improving the development of MW technology for the production of materials with enhanced properties.

Microwave irradiation has been proven to be an effective heating source in synthetic chemistry, and can accelerate the reaction rate, provide more uniform heating and help in developing better synthetic routes for the fabrication of bone-grafting implant materials. In this study, a new technique, which comprises microwave heating and powder metallurgy for in situ synthesis of Ti/CaP composites by using Ti powders, calcium carbonate (CaCO 3 ) powders and dicalcium phosphate dihydrate (CaHPO 4 ·2H 2 O) powders, has been developed. Three different compositions of Ti:CaCO 3 :CaHPO 4 ·2H 2 O powdered mixture were employed to investigate the effect of the starting atomic ratio of the CaCO 3 to CaHPO 4 ·2H 2 O on the phase, microstructural formation and compressive properties of the microwave synthesized composites. When the starting atomic ratio reaches 1.67, composites containing mainly alpha-titanium ( α -Ti), hydroxyapatite (HA), beta-tricalcium phosphate ( β -TCP) and calcium titanate (CaTiO 3 ) with porosity of 26%, pore size up to 152 μm, compressive strength of 212 MPa and compressive modulus of 12 GPa were formed. The in vitro apatite-forming capability of the composite was evaluated by immersing the composite into a simulated body fluid (SBF) for up to 14 days. The results showed that biodissolution occurred, followed by apatite precipitation after immersion in the SBF, suggesting that the composites are suitable for bone implant applications as apatite is an essential intermediate layer for bone cells attachment. The quantity and size of the apatite globules increased over the immersion time. After 14 days of immersion, the composite surface was fully covered by an apatite layer with a Ca/P atomic ratio approximately of 1.68, which is similar to the bone-like apatite appearing in human hard tissue. The results suggested that the microwave assisted- in situ synthesis technique can be used as an alternative to traditional powder metallurgy for the fabrication of Ti/CaP biocomposites.

Titanium is widely used in biomedical implants because of its excellent mechanical properties, good biocompatibility and high resistance to corrosion. However, the fabrication of titanium components often involves high cost due to the long processing time and difficulty in metalworking. Powder metallurgy is a near-net-shape processing method which has the advantage of high production rate with low unit cost. In this study, a technique comprising microwave sintering with powder metallurgy has been developed to fabricate titanium components. Commercially pure titanium powdered compacts, prepared by three initial particle size groups of 10±2 μm, 30±2 μm, and 50±2 μm, were sintered in a 1.4 kW, 2.45 GHz microwave multi-mode furnace for 2 minutes using silicon carbide particles as the microwave susceptor to assist the heating. The room temperature deformation behavior of titanium components was investigated. Metallographic studies of the porosity and pore size were undertaken by optical microscopy. The results of this study indicate that irregular shaped pores were uniformly distributed within the sintered specimens. Furthermore, the pore size and porosity of the sintered specimens decrease with decreasing initial particle size. The compressive yield strength showed a linear relationship with the porosity, and was found to follow the Hall-Petch relationship with the initial particle size. This study demonstrated that it is feasible to microwave sinter titanium components having various compressive yield strengths by controlling the initial powder size of the titanium.

The rapid in situ formation of a Ti alloy/TiC porous composite was achieved using the powder metallurgy approach. Ti6Al4V powders were mixed with 14.5 vol.% of multiwalled carbon nanotubes (MWCNTs) and the particle size of Ti6Al4V was reduced to ∼5 μm by ball milling. The MWCNTs acted as microwave susceptors as well as reactants for the rapid sintering of Ti alloys. The green compact of the Ti6Al4V/MWCNTs powder was sintered in a 1.4 kW, 2.45 GHz bi-directional microwave emission furnace without using any protective gas environment. The microwave sintering was completed within 2 min. The surface temperature of the sample reached 1620 °C during sintering, as measured by a pyrometer. Titanium carbide was formed after the sintering as confirmed by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The composite has a porosity of approximately 25%, compressive strength of 270.41 ± 24.97 MPa, compressive yield stress of 145.48 ± 27.28 MPa, compressive Young’s modulus of 10.87 ± 2.46 GPa and compressive strain of 3.75 ± 1.11%. The Vickers hardness value in the TiC region (545.4 ± 13.9 HV) is significant higher than that in the Ti alloy region (435.9 ± 12.9 HV). An overall Rockwell hardness of 47 HRA was measured.

Failure of the bone-implant interface in a joint prosthesis is a main cause of implant loosening. The introduction of a bioactive substance, hydroxyapatite (HA), to a metallic bone-implant may enhance its fixation on human bone by encouraging direct bone bonding. Ti6Al4V/TiC/HA composites with a reproducible porous structure (porosity of 27% and pore size of 6-89 μm) were successfully fabricated by a rapid microwave sintering technique. This method allows the biocomposites to be fabricated in a short period of time under ambient conditions. Ti6Al4V/TiC/HA composites exhibited a compressive strength of 93 MPa, compressive modulus of 2.9 GPa and microhardness of 556 HV which are close to those of the human cortical bone. The in vitro preosteoblast MC3T3-E1 cells cultured on the Ti6Al4V/TiC/HA composite showed that the composite surface could provide a biocompatible environment for cell adhesion, proliferation and differentiation without any cytotoxic effects. This is among the first attempts to study the in vivo performance of load-bearing Ti6Al4V/TiC and Ti6Al4V/TiC/HA composites in a live rabbit. The results indicated that the Ti6Al4V/TiC/HA composite had a better bone-implant interface compared with the Ti6Al4V/TiC implant. Based on the microstructural features, the mechanical properties, and the in vitro and in vivo test results from this study, the Ti6Al4V/TiC/HA composites have the potential to be employed in load-bearing orthopedic applications.