Effect Of Post-deposition Heat Treatment Research Articles

Effect of post-deposition heat treatment on microstructure and mechanical properties of NASA HR-1 cold spray coatings

The primary goal of this work was to examine the impact of heat treatment on the evolution of microstructure and mechanical properties of NASA HR-1 cold spray coatings. Coatings were produced employing a high-pressure cold spray system using N2 and He process gases and the effect of process gas and deposition temperature on the microstructure and mechanical properties of the coatings was examined. Microstructural characterization was performed using optical microscopy, scanning electron microscopy, micro X-ray computed tomography, and electron backscatter diffraction. NASA HR-1 coatings produced with He process gas exhibited improved plastic deformation and resulted in the lowest porosity compared to those deposited with N2 process gas. All coatings showed brittle failure with limited ductility in the as-deposited condition. Heat treatment of the NASA HR-1 cold spray coatings was performed at 550 °C and 950 °C for 1 h to improve the mechanical strength of the coatings. Heat treatment improved the particle bonding and enhanced the mechanical properties of the cold spray coatings. Heat treatment performed at 550 °C resulted in higher mechanical strength of coatings, whereas the heat treatment performed at 950 °C resulted in recrystallized microstructure and improved ductility of the coatings. However, heat treatment at 950 °C resulted in forming the Eta (η) phase and Ni-Ti intermetallics in all the NASA HR-1 cold spray coatings. The overall results suggest that using He as process gas contributed to reduced porosity and enhanced mechanical properties of the cold spray coatings.

Effect of Post-Deposition Heat Treatment on the Mechanical Behavior and Deformation Mechanisms of a Solid-State Additively Manufactured Al–Mg–Si Alloy

Abstract The effects of post-deposition heat treatment on the fatigue behavior of AA6061 processed by additive friction stir deposition (AFSD) were investigated for the first time in this work. A heat treatment to recover the T6 temper was performed on AFSD AA6061 is then subjected to strain-controlled fatigue and monotonic tension testing. Microstructural analysis revealed abnormal grain growth resulting in bimodal grain size distribution. Mechanical testing indicated a full recovery of the strength of the AA6061-T6 temper with comparable fatigue performance to the as-deposited AFSD AA6061. Fractography revealed deformation mechanisms in the post-deposition heat treatment not observed in the as-deposited samples, however, the fatigue resistance remained unchanged. A microstructure-sensitive fatigue model was implemented to capture the effects of the heat treatment process on the fatigue performance of the post-deposition heat-treated AFSD AA6061.

Effects of annealing temperature on microstructure and mechanical properties of cold sprayed AA7075

This paper examines the softening behaviour of cold sprayed 7075 aluminum alloy after isothermal annealing. The as-received powder was deposited by a high-pressure cold spray device using heated nitrogen as propellant gas. To investigate the effects of post-deposition heat treatment, the excised samples were isochronally annealed in the temperature range of 200 to 400°C. The feedstock powder and the free-standing coatings were initially characterized through various electron microscopy techniques (SEM, EDS, EBSD) and relevant microstructural features were determined. Mechanical properties of the as-sprayed and heat-treated samples were evaluated by quasi-static tensile and microhardness testing. It has been shown that extensive plastic deformation during cold spraying resulted in a dense coating with relatively low internal porosity. Specimens in an as-deposited state possessed a high level of strain hardening and exhibited a brittle rupture associated with intersplat cracking. When subjected to heat treatment, the cold spray deposits showed a general trend of microhardness reduction and progressive sintering of the microstructure with increasing annealing temperature. Furthermore, post-mortem observation revealed a gradual transition in fracture mechanism, manifested by improving material ductility and the occurrence of typical dimple morphology. The aspects responsible for the softening of the cold sprayed 7075 alloys are discussed further.

Effect of heat treatment on the microstructure and mechanical properties of AZ80M magnesium alloy fabricated by wire arc additive manufacturing

To maximize the benefits of wire arc additive manufacturing (WAAM) processes, the effect of post-deposition heat treatment on the microstructure and mechanical properties of WAAM AZ80M magnesium (Mg) alloy was investigated. Three different heat treatment procedures (T4, T5 and T6) were performed. According to the results, after T4 heat treatment, the microsegregation of alloying elements was improved with the eutectic structure dissolved. Samples after T5 heat treatment inherited the net-like distribution of secondary phases similar to the as-deposited sample, where the eutectic structure covering the interdendritic regions and the β-phase precipitated around the eutectic structure. After T6 heat treatment, the tiny β-phases re-precipitated from the matrix and distributed in inner and outer of the grains. The hardness distribution of the samples went through T4 and T6 heat treatment was more uniform in comparison to that of T5 heat treated samples. The tensile test showed that the T6 heat treatment improved the strength and ductility, and the anisotropy between horizontal and vertical can be eliminated. Moreover, T4 treated samples exhibited highest ductility.

Extensive Analysis on the Effects of Post-Deposition Annealing for ALD-Deposited Al2O3 on an n-Type Silicon Substrate.

In this study, an investigation was performed on the properties of atomic-layer-deposited aluminum oxide (Al2O3) on an n-type silicon (n-Si) substrate based on the effect of post-deposition heat treatment, which was speckled according to ambient temperature and treatment applied time. Based on these dealings, a series of distinctions for extracted capacitance and dielectric constant, hysteresis was performed on annealed and nonannealed samples. The interface and border trap responses, including stress behavior after an application of constant voltage for a specific time and surface morphology by X-ray diffraction (XRD) technique, were also analyzed between the two above-mentioned sample types. Based on observation, the annealed samples showed superior performance in every aspect compared with the nonannealed ones. Some unusual behaviors after high annealing temperature were found, and the explanation is the ion diffusion from oxide layer towards the semiconductor. Since a constant voltage stress was not widely used on the metal–oxide–semiconductor capacitor (MOSCAP), this analysis was determined to reveal a new dimension of post-deposition annealing condition for the Al/Al2O3/n-Si gate stack.

Effects of post-deposition heat treatment on nanostructured TiO2-C composite structure and antimicrobial properties

The growth of cases of nosocomial infections is an urgent issue in health care facilities. Reducing cross-contamination from high-frequency touch surfaces is a key area of interest. Robust TiO2 coatings on touch surfaces could reduce pathogen viability if the material could be modified to increase photocatalytic activity (PCA) under visible light. Research has focused on increasing the bandgap by use of dopants and rutile-anatase heterojunctions, using nanoparticles to increase active surface area, and sensitizing TiO2 with carbon. We have previously reported 11 μm thickness nanostructured anatase and rutile mixed phase TiO2 and carbon composite coatings (NsARC) which are antimicrobial under visible light. Here we investigate the role of the co-deposited carbon in the antibacterial performance. Coatings of 4.0–6.0 μm thicknesses nanostructured anatase were deposited by pulsed-pressure metalorganic chemical vapor deposition (pp-MOCVD) on stainless steel and glass substrates, and one set was heat-treated to remove the co-deposited amorphous carbon. Morphology, phase and adhesion were not affected by the short heat treatment at 500 °C in air. The water contact angle was reduced under visible light to a much greater extent for the carbon-free sample. The antimicrobial performance of the coatings was marginally enhanced by removing the carbon. While the carbon may be enhancing the visible light PCA of the TiO2, we conclude that it is also interfering with the transport of radical oxygen species to the bacteria and reducing the active surface area.

Effect of post-deposition heat treatment on laser-TIG hybrid additive manufactured Al-Cu alloy

ABSTRACT After solution + artificial aging treatment (T6 heat treatment) of 2219 aluminum alloy fabricated by laser-tungsten inert gas (TIG) hybrid method, more interestingly, we found that both the strength and elongation were improved. The strengthening mechanism has been analysed in details. Results showed that each layer was divided into the arc zone (AZ) and laser zone (LZ) before and after heat treatment. After T6 heat treatment, the columnar crystal grain morphologies remained the same as the as-deposited condition, while the microstructure presented a strong {001} texture along the building direction. Moreover, the high density of the needle-shaped θ″ phases were uniformly precipitated after artificial aging. Distinct grain morphology, increased the mass fraction of Cu in the Al matrix, and nano-precipitates in the AZ and LZ improved the tensile properties, which exhibited a yield strength of 242.1 ± 19.6 MPa, an ultimate tensile strength of 407.1 ± 31.1 MPa, respectively.

Effects of post-deposition heat treatment on microstructures of GTA-additive manufactured 2219-Al

ABSTRACTSeveral 2219-Al parts were produced by GTA (Gas Tungsten Arc) additive manufacturing, then an exceptional heat treatment characterised by long solution time was proposed and carried out to improve their microstructures and mechanical properties. Results show that, for the macroscopic features, the regional-division and layered-division features are eliminated after the heat treatment. For the microstructures, grain morphologies remain almost the same after the heat treatment, but the sizes and distributions of both eutectics and particles change significantly. The net-like and bulk-like eutectics are dissolved into point-like structures, while uniformly distributed θ′ – particles precipitate out. For the hardness, the heat treatment brings about significant precipitation strengthening, leading to a 97% increase of the Vickers hardness of GTA-additive manufactured 2219-Al.

Microstructure and mechanical properties of as-built and heat-treated electron beam melted Ti–6Al–4V

ABSTRACTThis paper investigates the effect of post-deposition heat treatment on porosity, microstructure, and mechanical properties of Ti–6Al–4V produced via an Electron Beam Melting process. Samples were studied in the conditions of as-built and heat treated at 920°C and 1030°C. The as-built samples were characterised by columnar β grains consists of α+β microstructure with Widmanstätten and colony morphologies were found. Heat treatment resulted in increased α lath width. The yield strength and ultimate tensile strength was greater in the as-built condition than wrought material. Porosity re-growth occurred after heat treatment but it did not affect the tensile properties. Greater ductility after heat treatment was attributed to the larger α lath width which increases effective slip length.

Mechanical Properties of Tool Steels with High Wear Resistance via Directed Energy Deposition

This study focused on the mechanical and metallurgical characteristics of high-wear-resistance steel (HWS) deposited using directed energy deposition (DED) for metal substrate hardfacing or repairing. As post-deposition heat treatment changes the metallurgical characteristics of deposits, the effect of post-deposition heat treatment on the mechanical properties was investigated via microstructure observation and by conducting hardness, wear, and impact tests. The obtained micro-images showed that the deposited HWS layers exhibit cellular and columnar dendrites, and the microstructure of heat-treated HWS (HT-HWS) transformed its phase during quenching and tempering. The hardness and wear resistance of the HT-HWS deposits were higher than those of the HWS deposited specimen, whereas the latter exhibited a higher fracture toughness. The matrix microstructure and carbide characteristics, which are characterized by the chemical composition of the materials, significantly influenced the mechanical properties.

Influence of heat treatment on wear behavior and impact toughness of AISI M4 coated by laser melting deposition

This study focuses on post-deposition heat treatment for possible hardfacing of cold press dies using M4 high-speed tool steel. For the experimental investigations, using the direct energy deposition (DED) process, powdered AISI M4 (a high-speed tool steel) is deposited on a substrate of AISI D2 (a general-use die steel). Since the post-deposition heat treatment may change the metallurgical characteristics of the deposits, the effect of post-deposition heat treatment on the mechanical behavior was investigated by observing the microstructure evolution, hardness, wear behavior, and Charpy impact tests of the specimens with different post-deposition heat treatments. The experimental results showed that post-deposition quenching and tempering led to a reduction in hardness, which was attributed to the relieved residual stress, tempered martensite, and removal of carbon from the martensite during tempering. The M4-deposited specimen without post-deposition heat treatment and the tempered M4-deposited specimen had the better wear resistance, compared to the quenched–tempered M4-deposited specimen with fine carbides. Nevertheless, the toughness increased significantly in the quenched and tempered specimen. The results presented in this paper provide guidelines for practical hardfacing applications that use high-alloy tool steel powders to achieve highly improved die and mold performances in terms of wear resistance and toughness.

Effects of postdeposition heat treatment on the structural and magnetic properties of CoFe2O4 nanoparticles produced by pulsed laser deposition

In this work, we investigated the effects of postdeposition heat treatment on structural and magnetic properties of CoFe2O4 nanoparticles produced by pulsed laser deposition. Structural analysis by X-ray diffraction, transmission electron microscopy (TEM) and Mössbauer spectroscopy indicate the formation of a single phase cobalt ferrite nanoparticles with the size ranging from 4.3 to 33.3 nm depending on the annealing temperature. The magnetic properties of the samples were investigated in a wide temperature range (50–400 K). Noticeable effects of the cubic magnetocrystalline anisotropy on the magnetization process of nanoparticles were observed for samples annealed at 450 °C and 600 °C, while for samples as-deposited and annealed at 300 °C the magnetization properties were dominated by a uniaxial effective anisotropy. ΔM technique was used to investigate the magnetic interaction among the nanoparticles. Only demagnetizing interactions were observed for the sample annealed up to 300 °C, while for the samples treated at 450 °C and 600 °C, both magnetizing and demagnetizing interactions were observed. The results are discussed considering the evolution of the nanoparticles' nanostructure with anneals and its effects on the magnetic properties.

Effect of post-deposition heat treatment on electrodeposited NiCoCrAlY coatings

An electrolytic process was utilised to fabricate NiCoCrAlY coatings, involving deposition of a composite coating consisting of the (Ni,Co) matrix and CrAlY particles, followed by a diffusion heat treatment to convert the composite coating to the desired NiCoCrAlY microstructure. This study focused on the effects of the post-deposition heat-treating conditions (temperature and atmosphere) on the final coating microstructure and composition. The (Ni,Co)–CrAlY composite coatings were heat-treated for 2 h at 1000, 1100 and 1200°C in vacuum and Ar, respectively. Phase constituents and concentrations of the major elements in the coating after heat treatment were examined. Vacuum heat treatment at temperatures ≥1100°C resulted in a significant decrease in Cr content at the coating surface due to Cr evaporation. Heat treatment at 1200°C also caused outward diffusion of Ti from the substrate alloy to the coating layer.

Microstructure Evolution, Tensile Properties, and Fatigue Damage Mechanisms in Ti-6Al-4V Alloys Fabricated by Two Additive Manufacturing Techniques

Additive Manufacturing (AM) technology is capable of building 3D near-net-shaped functional parts directly from computer models, using unit materials, such as powder or wire. AM offers superior geometrical flexibility with significantly reduced manufacturing lead time, energy, and material waste. These benefits make AM desirable for critical transportation applications, providing that structural integrity and performance requirements are met or exceeded. In this study, structural materials fabricated by two AM techniques were investigated: Laser Engineered Net Shaping (LENS) and Electron Beam Melting (EBM). Ti-6Al-4V alloys were produced using both methods and various processing conditions, which resulted in different microstructures and mechanical properties given their unique thermal histories. Characteristic microstructures were determined for all cases. Room temperature tensile and fatigue crack growth (FCG) properties were also evaluated and compared in different orientations with respect to the deposition direction. The effects of post-deposition heat treatment on tensile and FCG properties were determined. The results are systematically presented and discussed from both the material/process optimization, as well as structural design and fatigue life prediction perspectives.

Optical properties on thermally evaporated and heat-treated disodium phthalocyanine derivative thin films

Thin films were grown on quartz substrates and crystalline silicon wafers using disodium phthalocyanine and the organic ligands 2,6-diaminoanthraquinone, 2,6-dihydroxianthraquinone and its potassium derivative salt. The surface morphology of these films was analysed by atomic force microscopy (AFM) and scanning electron microscopy (SEM). IR spectroscopy was employed in order to investigate possible changes of the intra-molecular bonds between the powder compounds and thin films. The optical parameters have been investigated using spectrophotometric measurements of absorbance in the wavelength range of 200–1100 nm and the effects of post-deposition heat treatment were analysed. The absorption spectra recorded in the UV-Vis region for the deposited samples showed two bands, namely the Q and Soret bands. The absorption coefficient in the absorption region reveals non-direct transitions. In addition, the optical gap dependence upon the thickness of these thin films was evaluated.

Effect of Annealing on Microstructure of Hydroxyapatite Coatings and their Behaviours in Simulated Body Fluid

In this study, hydroxyapatite (HA) coatings on Ti6Al4V substrate were deposited using an ion beam sputtering technique. Owing to its medical applications, the crystalline phases present in the HA must be controlled. This study investigated the effect of post-deposition heat treatment at different temperatures and evaluated the microstructure of the HA coatings and their behaviours in simulated body fluid (SBF). The post-deposition treatment of the as-deposited samples was carried out in an air-circulated furnace at a temperature between 300 0C and 600 0C. The XRD patterns reveal that the minimum temperature to transform the HA coating from amorphous to crystalline phase is 400 0C. A higher temperature at 600 0C leads to a growth of the crystalline HA phases. Fourier transform infrared spectroscopy (FTIR) measurements show the existence of hydroxyl and PO-bonds in all coatings and the amounts varied with temperature. Atomic Force Microscopy (AFM) study suggests that the nanostructured crystalline HA starts to grow at 400 0C and becomes more obvious at a higher temperature of 600 0C. The simulated body fluid (SBF) test reveals that better apatite formation with post deposition heat treatment at 600 0C would potentially enhance the formation of new bone (osseointegration).

Effect of heat treatment on the structural and optical characteristics of plasma deposited 2-(diethylamino)ethyl methacrylate thin films by a capacitively coupled glow discharge plasma system

This paper reports the effect of post-deposition heat treatment on the optical and structural properties of plasma polymerized 2-(diethylamino)ethyl methacrylate (PPDEAEMA) thin films. SEM confirm that both as-deposited and heat treated PPDEAEMA thin films are uniform and pinhole free. Differential thermal analysis and thermogravimetric analysis demonstrate the decomposition and mass loss of PPDEAEMA, respectively, and PPDEAEMA is stable up to 550 K. The Fourier transform infrared spectroscopic investigation indicates the presence of the –CH2– group in as-deposited PPDEAEMA and heat treated PPDEAMEA. The absorption coefficient, allowed direct transition, Eqd, and allowed indirect transition, Eqi, energy gaps were determined from the ultraviolet–visible absorbance spectra and thus the Urbach energy, steepness parameter and extinction coefficient were calculated. Eqd and Eqi decrease with an increase in thickness and are found to be about 3.25–3.45 and 1.65–1.90 eV, respectively, for as deposited PPDEAEMA thin films of different thicknesses. The effect of heat treatment on the optical properties in relation to structural changes of PPDEAEMA is also discussed. As temperature increases, both Eqd and Eqi decrease. The Urbach energy Eu of the PPDEAMEA thin films increases with the increase in film thickness and heat treatment temperature. The steepness parameter β decreases with thickness and heat treatment temperature.

Effects of post-deposition heat treatment on the microstructure and properties of Al-doped ZnO thin films prepared by aqueous phase deposition

In this study, transparent conducting aluminum-doped ZnO thin films (AZO) were deposited on glass substrates by a water-based liquid phase deposition method. The results show that by employing a two-step post-deposition heat treatment, the preferential orientation of ZnO (002) appeared as soon as the polycrystalline films were formed. Under a reducing atmosphere, the crystallinity of the films was effectively improved. Furthermore, the reducing atmosphere was also beneficial for the removal of the residual stress of the prepared films and the c-axis lattice constant was less stretched as compared to those under an inert atmosphere at identical Tp. Both the atomic force micrograph and scanning electron micrograph clearly exhibited that the heat treatment induced considerable grain growth. The X-ray photoelectron spectrum revealed that the heat treatment atmosphere had little impact on the bonding state of zinc and that the reducing atmosphere was favorable for the non-stoichiometric alumina, which in turn, resulted in more oxygen vacancies and led to improvement in electrical conductivity. The ratio of chemisorbed oxygen declined substantially when applying the reducing atmosphere. Accordingly, hydrogen was helpful for the reduction of chemisorbed oxygen onto AZO films. Generally, the electrical resistivity declined linearly with Tp. A minimum resistivity of 9.90×10−3Ω·cm was obtained with a doping concentration of Al/Zn=2.25at.% at Tp=700°C. The largest mean free path of the carriers was 1.2Å, which was much smaller than the observed grain sizes of the AZO films. Accordingly, the grain boundary scattering was not the detrimental scattering mechanism. In contrast, the scattering within the grains was responsible for the low mobility. An increase in optical transparency with the heat treatment temperature was observed due to the compact and smooth topography with larger grains, among which, less porous structures were formed at elevated temperature.

High Efficiency Sputtered CdS/CdTe Cells without CdCl2 Activation

ABSTRACTPolycrystalline thin-film CdS/CdTe PV cells nearly always require “activation” with vapors containing chlorine and oxygen near 400 oC in order to realize the highest cell performance, even when growth occurs near 600 oC. In this study we have used film growth near 270 oC by magnetron sputtering in an oxygen-free ambient and have studied the effects of post-deposition heat treatments for 20 minutes at 400, 425 and 450 oC without CdCl2 in a dry air ambient. The heat treatments enhanced grain growth and produced re-crystallization of the CdTe film at all three temperatures, but 450 oC was required to reach the best electrical performance. Grain size increased from a couple of hundred nanometers to more than a micron as the preferred (111) growth orientation decreased. Efficiencies up to 11.6% were achieved with no CdCl2 compared to ~13% with activation at 387 oC in the presence of CdCl2 vapors. X-ray diffraction and quantum efficiency measurements show interdiffusion of CdS and CdTe at 450 oC comparable with a standard CdCl2 treatment at 387 oC. The results are discussed in terms of CdSTe alloy gradients and minority-carrier diffusion lengths.

Effect of heat treatment on mechanical dissipation in Ta2O5 coatings

Thermal noise arising from mechanical dissipation in dielectric reflective coatings is expected to critically limit the sensitivity of precision measurement systems such as high-resolution optical spectroscopy, optical frequency standards and future generations of interferometric gravitational wave detectors. We present measurements of the effect of post-deposition heat treatment on the temperature dependence of the mechanical dissipation in ion-beam sputtered tantalum pentoxide between 11 K and 300 K. We find that the temperature dependence of the dissipation is strongly dependent on the temperature at which the heat treatment was carried out, and we have identified three dissipation peaks occurring at different heat treatment temperatures. At temperatures below 200 K, the magnitude of the loss was found to increase with higher heat treatment temperatures, indicating that heat treatment is a significant factor in determining the level of coating thermal noise.