Influence Of Post-deposition Heat Treatment Research Articles

Influence of Post-Deposition Heat Treatments on the Microstructure and Tensile Properties of Ti-6Al-4V Parts Manufactured by CMT-WAAM

Cold metal transfer (CMT)-based wire and arc additive manufacturing (WAAM) of Ti-6Al-4V alloy has been investigated to manufacture walls with two different building strategies. This study focuses on the influence of the application of thermal treatments on the resulting microstructure and mechanical properties. Deep microstructural analysis revealed different grades of growth of lamellae α phase after several thermal treatments at different temperatures, which lead to different tensile mechanical properties and better strength and ductility balance compared to the as-built condition. Results are compared with equivalent forged and casting standards and the state of the art for WAAM of Ti-6Al-4V alloy. At temperatures of 920 °C, anisotropy was maintained and elongation increased by 70% while yield strength and UTS was slightly decreased by 8%.

Influence of Post-deposition Heat Treatments on the Microstructure and Mechanical Properties of Wire–Arc Additively Manufactured ATI 718Plus

To maximize the benefits of additive manufacturing (AM) processes, optimizing the as-processed microstructure and its associated mechanical properties through post-deposition heat treatment is important. The present study investigates the influence of post-deposition heat treatments on the microstructure and mechanical properties of wire–arc additively manufactured (WAAM) ATI 718Plus. The application of the standard heat treatment recommended for the wrought ATI 718Plus led to the formation of excessive eta (η) phase particles along the interdendritic spaces. This microstructure degrades the tensile properties of the WAAM condition and exhibits a profound anisotropic effect. To enhance the microstructure for improved properties, the nature of the submicron-sized particles that formed within the microstructure is identified. Experimental and thermodynamic simulation tools are utilized to develop time–temperature-transformation (TTT) diagrams, and the growth kinetics of η phase in the WAAM ATI 718Plus is determined. Based on the analyses, appropriate heat treatments capable of precipitating a moderate amount of η phase are designed and evaluated. The newly developed heat treatment significantly improves the mechanical properties of the AM alloy and reduces the anisotropic effect.

Effect of heat treatment on microstructure and mechanical properties of the selective laser melting processed Ti-5Al-2.5Sn α titanium alloy

In the present work, selective laser melting technology (SLM) has been used to produce Ti-5Al-2.5Sn α titanium alloy and the influence of post-deposition heat treatments on microstructure and mechanical properties of the as-deposited alloy has been in-depth analyzed for the first time. As-deposited Ti-5Al-2.5Sn exhibits a columnar prior-β microstructure with martensitic α′ needles filled inside and a small amount of grain-boundary α (αGB) stripes precipitated at the prior-grain boundaries. After subtransus heat treating at 600°C to 750°C for 2h, incomplete recrystallization of the as-deposited microstructure occurs and the recrystallized α grains with equiaxed morphology nucleate mainly through grain boundary migration of the stripe-like αGB, leading to a duplex microstructure composed of the soft recrystallized α and 75.1–97.6% high-strength α′. After subtransus heat treating at 850°C to 950°C for 2h, complete recrystallization of the as-deposited microstructure occurs and the coarsening of recrystallized α grains becomes more pronounced at 950°C. By contrasting, an excessively coarsened widmanstatten microstructure composed of α laths with lengths up to several hundred micrometers has been obtained after supertransus heat treating at 1100°C for 2h. Both of the as-deposited and heat-treated samples exhibit relatively weak textures, resulting in very little mechanical anisotropies. Because of the dominant α′ microstructure, as-deposited possesses ultrahigh tensile strengths but also a poor elongation (7.7–8.2%) in comparison to the conventionally-fabricated Ti-5Al-2.5Sn. After the heat treatments, tensile strengths gradually decrease whereas elongation increases first and then decreases with the elevating annealing temperature, reaching its peak at 750°C (14.4–15.2%). Finally, it has been proved that both elongations and tensile strengths of the 650–850°C/2h heat-treated samples can exceed those of the conventionally-fabricated Ti-5Al-2.5Sn. These findings provide some basis for the rapid fabrication of high-strength α titanium alloy products with a satisfactory ductility.

Influence of Post-deposition Heat Treatments on the Optical Properties of Chemically Deposited Nanocrystalline TiO2 Thin Films

The aim of this study is to investigate the potentials of TiO2 thin films for device applications. Nanocrystalline single phase of rutile TiO2 thin films have been prepared by Chemical Bath Deposition (CBD) technique at bath temperature range from 75-80C, keeping other deposition variables constant. The films were then subjected to post-deposition heat treatments with annealing temperatures in the range 373 to 673 K. The optical characterisation was done using the Elmer Lambda-2 spectrometer to investigate the transmittance and absorbance versus wavelength measurements. The data obtained from the transmittance and absorbance measurements were used to deduce the important optical constants. The results show that the energy bandgap was direct, with values in the range ≤1.8 eV for the as-deposited layers and ≥2.2 eV for the annealed layers. At lower temperatures, the band gaps of the annealed samples did not differ significantly from the energy gap (1.8 eV) of the as-deposited film. At higher thermal treatment, the energy gaps increased with the increase in annealing temperatures and a maximum of 2.2 eV for the energy gap was determined for TiO2 film annealed at 673 K. The values of the energy bandgap obtained in study, are within the range suitable for application in photovoltaic solar cell devices and in related photonic applications.

The effect of inter-layer cold working and post-deposition heat treatment on porosity in additively manufactured aluminum alloys

Wire+Arc Additive Manufacture (WAAM) has been shown to be suitable for manufacturing large-scale metallic parts. However porosity in the deposited aluminum material restricts the application of WAAM for aluminum alloys. In this study inter-layer rolling process was employed during the deposition of aluminum alloys and its influence on porosity was investigated. Samples of straight walls were prepared with both the 2319 aluminum alloy wire and the 5087 aluminum alloy wire. Inter-layer rolling was employed between each and every deposited layer. Different rolling loads of 15kN, 30kN and 45kN were applied, greatly reducing the quantity of the pores for both alloys. With a rolling load of 45kN the pores larger than 5μm in diameter were eliminated. In additional, the influence of post-deposition heat treatment on porosity was investigated on the as-deposited samples as well as on the samples built with inter-layer rolling of 45kN load. A different behavior of pores’ formation and growth was found between 2319 alloy and 5087 alloy, both for as-deposited status and heat-treated status. Post-deposition heat treatment increased the area of the pores for both alloys. After the post-rolling heat treatment, no pores larger than 5μm in diameter was found re-initiated for both alloys.

Influence of post-deposition heat treatment on optical properties derived from UV–vis of cadmium telluride (CdTe) thin films deposited on amorphous substrate

In this work, we report on post-deposition heat treatment (annealing)-induced change in optical properties derived from UV–vis study of CdTe thin films prepared on amorphous glass substrate by electron beam evaporation technique. Annealing effect gives rise to the enhancement in crystalline nature (zinc blende structure) of CdTe films with (111) preferred orientation. The average transmittance was increased with the annealing temperature and the slight shift in transmission threshold towards higher wavelength region revealed the systematic reduction in optical energy band gap. The existence of shallow level just below the conduction band, within the band gap was identified in the range of 0.23 and 0.14eV for the films annealed at 200 and 450°C, respectively. The optical quality of deposited films was confirmed by the photoluminescence study. In addition, the scanning electron microscopic measurement supports the result of X-ray diffraction study. The Swanepoel, Hervé-Vandamme, and Wemple−DiDomenico models have been employed to evaluate the various optical parameters of CdTe films. These results are correlated well with other physical properties and discussed with the possible concepts underlying the phenomena.

Influence of post-deposition heat treatment on electrical transport properties of In2S3-buffered Cu(In,Ga)Se2 cells

The electrical characteristics of Cu(In,Ga)Se2-based solar cells with In2S3 buffer were investigated. The effects of post-deposition annealing in helium or in air on current–voltage characteristics, net acceptor density profiles and admittance spectra were studied. Analysis of the current–voltage characteristics showed that interface recombination dominated transport in the as-deposited devices was reduced after annealing and partially replaced by bulk recombination. This was accompanied by a decrease in the saturation current and diode ideality factor. The influence of the heat treatment on the buffer/hetero-interface region as determined by capacitance measurements was minor. We conclude that a reduction in the interface states density and in the p+ layer doping caused by the chemical modification of the hetero-interface region is the major source of the improvement.

The effect of geometry and post-annealing on surface acoustic wave characteristics of AlN thin films prepared by magnetron sputtering

This paper describes experimental relationship between surface acoustic wave (SAW) properties of two-port SAW resonators based on polycrystalline aluminum nitride (AlN) thin films grown on Si substrates by using a pulsed reactive magnetron sputtering system and their geometry's parameters. Moreover, the influence of post-deposition heat treatment on SAW properties of AlN thin films was investigated at different annealing temperature (600 °C and 900 °C). The measurement results show the number of the inter-digital transducers (IDT) finger pairs ( N), the number of reflectors grating pairs ( R) and the IDT center-to-center distance ( L) related to insertion loss of SAW resonators. The best result of insertion loss was 15.6 dB for SAW resonators with R = 160 pair, N = 5 pair and L = 750 μm. At the same geometry parameters, the SAW velocity and insertion loss were improved slightly after annealing at 600 °C and were worse for the films annealed at 900 °C by changes in the surface morphology and stress on the film.

YNi xMn 1− xO 3 thin films by pulsed laser deposition: Structure and magnetic properties

Highly oriented YNi x Mn 1− x O 3 thin films on SrTiO 3 (100) substrates were achieved by using pulsed laser deposition for x = 0.33 and x = 0.50. We used a combination of X-ray diffraction, scanning electron microscopy, atomic force microscopy, and magnetic-property measurements. The magnetic transition temperatures ( T c) of the as-grown films are higher than the corresponding bulk values (typically 85 K instead of 80 K, for x = 0.5, and 60 K instead of 50 K, for x = 0.33). Our magnetic measurements also suggest a spin-glass characteristic in the x = 0.33 films, while a cluster glasslike behavior is observed for the films with x = 0.5, which is quite different from that of the bulk samples. Finally, the influence of post-deposition heat treatment on the magnetic properties of the as-grown films is discussed.

XRD study of the grain growth in CdTe films annealed at different temperatures

Abstract The CdTe thin films electrodeposited on stainless steel substrates were annealed in air at various temperatures and time durations in order to investigate the influence of post-deposition heat treatments on the grain growth of the films. The recrystallization process at lower annealing temperature is different from that of the high-temperature annealing. The annealing at lower temperature promotes better grain growth by maintaining the preference for the (1 1 1) plane. In general the grain size increases due to annealing and the recrystallization happens in three phases. The grain growth exponent is a function of temperature and time. In the beginning of the annealing, irrespective of the annealing temperatures the grain growth obeys the ideal parabolic law and for longer annealing times it deviates from the ideal case.

The effect of annealing on the structure of CdTe films electro-deposited on metallic substrates

In this work we report the influence of post-deposition heat treatments on the structure of the CdTe films electro-deposited on stainless steel substrates. The CdTe films were annealed in air at various temperatures and time in order to investigate the influence of post-deposition heat treatments on the film structure. The various structural parameters, such as grain size, lattice constant and stress, were investigated using XRD. The results showed that the stress, grain growth and the re-crystallization of CdTe depends on the post-deposition annealing time and temperatures. In the initial stages of annealing when the grains grow in size, the grain growth process obeys a parabolic growth law. The re-crystallization process during annealing has two stages, in the beginning, the re-crystallization is dominated by random orientation of the grains followed by a second process in which once again the crystallites tend to orient in a particular direction. The value of activation energy for 20% re-crystallization in CdTe was estimated as 1.17±0.1 eV. The as-deposited film is under compressive stress and with annealing the compressive stress increases. For longer annealing times the stress changes from compressive to tensile. The calculated stress is ∼10 9 dyn/cm 2. Lattice parameter of the as-deposited film is larger than the powder sample and upon annealing lattice value increase and reaches a maximum and on further annealing for a long time it decreases and attains a value less than that of the powder sample. The calculated value of the change in band gap due to the stress, induced during the annealing, is in the range −13 meV⩽Δ E g⩽17 meV.

Optical properties of flash-evaporated CuIn 0.75Ga 0.25Se 2 thin films by photoacoustic spectroscopy

A high-resolution near-infrared photoacoustic spectrometer of the gas-microphone type is used for room-temperature analysis (in the subgap region of the spectrum) of non-radiative defect levels in as-grown CuIn 0.75Ga 0.25Se 2 thin films. Films were grown by flash evaporation onto glass substrates at 200 °C. The absorption coefficient has been derived from the photoacoustic spectra to determine the gap energy and establish the activation energies for several defect-related energy levels. We also present preliminary results relating to the influence of post-deposition heat treatments in a selenium atmosphere on the photoacoustic spectral response. The improvements in the photoacoustic spectrum following annealing are directly correlated with the sample compositional, structural and electrical properties. Finally, the effect of interference on the photoacoustic spectra is discussed.