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Large-scale industrial application of additively manufactured (AM) components in general, and specifically cold sprayed additive manufactured (CSAM), is limited due to the nature of this technology and the resulting product's porosity and embrittlement. To improve the final properties of additively manufactured material, many lengthy, complex, or expensive post-treatments have been proposed. Reducing the environmental impact, cost, and time required for additive manufacturing will allow for greater use in industrial applications. A novel thermomechanical treatment known as in situ electro-plastic treatment (ISEPT) is used in this study to treat CSAM Ti-6Al-4 V alloy known as grade 5 titanium. The Ti-6Al-4 V alloy has approximately three times the strength and hardness of commercial purity titanium (CP-Ti) with lower ductility and a dual-phase (α + β) microstructure that poses challenges during the CSAM process. Compared to CP-Ti, the results showed that CSAM Ti-6Al-4 V presented double the porosity and triple the number of ISEPT passes that presented ~ 2 µm ultra-fine grain microstructure. The ultimate tensile strength (UTS) of the ISEPT material was superior to that of CSAM Ti-6Al-4 V and increased from 184 to 1096 MPa with improved ductility rise from 1.1 up to 8.8%. Six ISEPT passes in air resulted in a slight increase in oxygen from 0.2% in the as-CSAM condition to 0.35%. Tensile properties of the ISEPT material were comparable to wrought Ti-6Al-4 V with 989 MPa UTS and 8.3% elongation. The ISEPT passes consolidated the CSAM (α + β) dual-phase Ti-6Al-4 V and allowed for the nucleation of equiaxed grains at the vicinity of former CSAM splat boundaries. The formation of lamellar colonies within the splat's inner regions was observed. The role of ISEPT conditions on the rapid elimination of porosity and the evolution of cold spray splat boundaries via dynamic recrystallization were discussed. [ABSTRACT FROM AUTHOR]

In this study, an in situ electro-plastic treatment (ISEPT) process was used to simultaneously eliminate porosity and brittleness in cold spray (CS) additive manufacturing (AM) of a grade 2 commercial purity titanium (CP Ti). The CS deposition conditions were optimized using a validated 3D CFD model to minimize oxidation while reducing porosity in the as-sprayed CP Ti. The ISEPT electric current and load were applied in the same direction (in situ) to improve the electro-plastic effect and to recrystallize CS CP Ti in an open-air environment. The rapid heating sourced from the applied current occurred at a temperature below 550 °C, the critical temperature for titanium oxidation, and at 24–30 mm/min deformation rate. The rapid nature of ISEPT treatment is associated with abolition of the necessary isothermal (oven) treatment for static recrystallization and corresponding time required for preheating in other rival thermomechanical treatments. The treated CP Ti structure exhibited transformation of CS splat structure to refined equiaxed grains. The porosity of the cold-sprayed structure was considerably reduced from 5 to as low as 0.1% after double ISEPT. The elongation was increased substantially from 0.5 for as-sprayed to 18% for the ISEPT-treated material. Similar improvements were observed in relation to CP Ti strength, hardness, and stiffness modulus. Results revealed that the ISEPT in the absence of controlled atmosphere contributed 0.06% to the Ti oxygen pick up, keeping the composition well within the acceptable range for CP Ti. The effect of ISEPT conditions on rapid elimination of porosity and progress of Ti recrystallization to cold-sprayed additively manufactured CP Ti has led to significant improvement in the material ductility in a short processing time at a relatively low temperature allowing elimination of costly controlled atmosphere. [ABSTRACT FROM AUTHOR]

Titanium and its alloys have been used in a broad range of products such as biomedical implants due to their high specific strength, corrosion resistance, and biocompatibility. Improvement in microstructure and mechanical properties of commercially pure (CP) titanium is usually performed by cold rolling and controlled atmosphere heat treatment. However, this is an energy-intensive, expensive, and a multi-stage process to achieve the desired properties. Hence, to address these challenges, in this study, the effects of an in situ electro-plastic treatment (ISEPT) on the microstructure evolution of CP titanium have been studied. The deformation load and electric current in this treatment were applied in the same direction (in situ) to maximize the electro-plastic effect. Simultaneous electric current and strain application created a condition for dynamic recrystallization to occur at low temperature and under atmospheric conditions, thus reducing the cost and energy for manufacturing in a single process. The rapid heating and cooling prevented the oxidation of titanium to a large degree, eliminating the requirements for costly inert gas or vacuum. The results showed rapid recrystallization of CP titanium at 3.2 mm/s roller surface speed. Recrystallization led to a reduction in average grain size to 7 μm with 18% increase in microhardness. Pre-cold rolling of the CP-Ti structure enhanced grain refinement due to the introduction of dislocations and the applied electric current interactions. The SEM and XRD investigations revealed the relationship between the ISEPT treatment and the evolution of microstructure in CP-Ti. The effect of specimen geometry on the ISEPT was discussed. [ABSTRACT FROM AUTHOR]

The influence of thermal interface resistance is an important design problem for the optimisation of heat transfer systems. For thermoelectric generators (TEG), it can limit the ability to convert thermal energy directly to electrical energy. This paper describes an experimental and numerical study of the influence of thermal interface resistance on TEG module performance. A test apparatus was constructed to evaluate TEGs under varying temperature and heat source/sink conditions. The effect of heat source/sink interface finish grades, corresponding to medium quality (N8-N6) and very fine (N5-N4) surface finishes, at varying clamp forces, is evaluated. Then the application of cold spray additive manufactured copper, as a novel method of TEG module thermal interfacing is explored. Experimental data is accompanied with numerical analysis using TEG ideal equations and the effective material properties approach with the incorporation of temperature dependency and fabrication quality factors to improve modelling accuracy. A system of simultaneous heat flow equations is then established to numerically solve for the presence of thermal interface resistance. The results show that high clamp forces (3600 N) and very fine finish grades were sufficient to minimise thermal interface resistance to the range 0–5.98 × 10 − 5 m 2 K W − 1 , representing a loss of 0–9.9% in maximal achievable power. For the cold spray thermally interfaced TEG module, resistance estimates were lower and in the range 0–5.4 × 10 − 6 m 2 K W − 1 , corresponding to a 0–1.0% loss in power. • Heat source/sink surfaces, with varying finishes (N8-N4) and clamp forces, are evaluated for influence on thermoelectric generator (TEGs) performance. • Cold spray additive manufacturing is proposed and experimentally evaluated as a novel method of TEG heat source/sink thermal interfacing. • A system of heat flow equations are used to solve for the presence of thermal interface resistance (R T I R) at TEG heat source/sink interfaces. • High clamp forces (3600 N) and very fine finishes (N4) minimised R T I R to the range 0–5.98 × 10 − 5 m 2 K W − 1 , representing a loss of 0–9.9% in maximal achievable TEG power. • R T I R estimates for the cold spray thermally interfaced TEGs were lower and in the range 0–5.4 × 10 − 6 m 2 K W − 1 , corresponding to a 0–1% loss in power. [ABSTRACT FROM AUTHOR]