In-situ comparison of deformation behavior at 23 ℃ and 650 ℃ of laser direct melting deposited Ti-6Al-4V alloy (original) (raw)
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The International Journal of Advanced Manufacturing Technology, 2020
Recent studies have shown that the mechanical properties of Ti alloys produced by additive manufacturing (AM) methods are sensitive to AM process parameters. The mechanical threshold stress (MTS) model is capable of predicting the flow stress behavior of materials; however, the parameters needed in the MTS model are affected by the microstructure that originates from the AM process parameters. To find a relationship between the AM process parameters and the MTS parameters, the effect of process parameters on the mechanical properties of selective laser-melted (SLM) Ti-6Al-4V samples was studied. As the MTS model is sensitive to the microstructure, only near fully dense samples were considered.
Journal of Materials Engineering and Performance, 2021
The microstructures and mechanical properties of Ti-6Al-4V fabricated using laser metal deposition (LMD) and electron beam melting (EBM) were investigated and compared. The hardness, strength and work hardening exponent (n) of the LMD samples are superior to that of EBM samples. The EBM samples are more ductile, exhibit resistance to rapid plastic strain localization and have uniform hardness throughout the build. A detailed microstructural characterization was conducted for both alloys before and after the tensile tests. The differences in mechanical behavior of the two samples originate from their distinct dislocation densities within a and the relative proportions of Widmanstätten and colony type arrangements of the a+b laths, which in turn are an outcome of the distinct cooling profiles in the two additive manufacturing methods. On the basis of these results, strategies to improve the mechanical properties of both alloys are discussed.
Journal of Materials Engineering and Performance
Additive manufacturing (AM) is defined as a technology performed for tooling applications. It is used for manufacturing tools that have complex shapes and figures. In this study, an extensively applied Ti-6Al-4V alloy was made using the selective laser melting method. Post-production heat treatments were applied to decrease thermal stresses and to enhance the mechanical properties and the microstructure. The study investigates the fatigue mechanical properties, microstructure, hardness, and porosity of the AM Ti-6Al-4V after stress relieving (SR) and after SR followed by hot isostatic pressing (HIP). The samples’ upper and lower parts were independently examined to determine the effects of thermal conditions and the heat treatment of the microstructure. The microstructures were examined through optical microscopy, scanning electron microscopy and x-ray diffraction methods. The mechanical properties were investigated through microhardness testing, alongside assessment by fatigue test...
Materials
An investigation of mechanical properties of Ti6Al4V produced by additive manufacturing (AM) in the as-printed condition have been conducted and compared with wrought alloys. The AM samples were built by Selective Laser Melting (SLM) and Electron Beam Melting (EBM) in 0°, 45° and 90°—relative to horizontal direction. Similarly, the wrought samples were also cut and tested in the same directions relative to the plate rolling direction. The microstructures of the samples were significantly different on all samples. α′ martensite was observed on the SLM, acicular α on EBM and combination of both on the wrought alloy. EBM samples had higher surface roughness (Ra) compared with both SLM and wrought alloy. SLM samples were comparatively harder than wrought alloy and EBM. Tensile strength of the wrought alloy was higher in all directions except for 45°, where SLM samples showed higher strength than both EBM and wrought alloy on that direction. The ductility of the wrought alloy was consist...
Materials (Basel, Switzerland), 2018
Additive manufacture (AM) appears to be the most suitable technology to produce sophisticated, high quality, lightweight parts from Ti6Al4V alloy. However, the fatigue life of AM parts is of concern. In our study, we focused on a comparison of two techniques of additive manufacture-selective laser melting (SLM) and electron beam melting (EBM)-in terms of the mechanical properties during both static and dynamic loading. All of the samples were untreated to focus on the influence of surface condition inherent to SLM and EBM. The EBM samples were studied in the as-built state, while SLM was followed by heat treatment. The resulting similarity of microstructures led to comparable mechanical properties in tension, but, due to differences in surface roughness and specific internal defects, the fatigue strength of the EBM samples reached only half the value of the SLM samples. Higher surface roughness that is inherent to EBM contributed to multiple initiations of fatigue cracks, while only...
Influence of Laser Treatment on the Creep of the Ti-6Al-4V Alloy
Metallurgical and Materials Transactions A, 2011
Titanium and its alloys are excellent materials for structural applications in components submitted to high temperatures because of their high strength, weight ratio, good corrosion resistance, and microstructural stability. However, the affinity to oxygen is one of the main factors that limit their application as structural materials at high temperatures. The objective of this work was to estimate the influence of laser treatment on the creep of a Ti-6Al-4V alloy. Constant load creep tests were conducted at 873 K (600°C) in a standard creep machine at a stress of 125 to 319 MPa. Samples with a gage length of 18.5 mm and a diameter of 3.0 mm were used for all tests. It was observed that the effect of the oxidation was smaller and the behavior of the creep curves showed that the life time in laser treated samples was better than in the received samples. An increase of ductility of final strain and in the lifetime for the lasertreated material was observed. The decrease of the steady-state creep occurred in conjunction with the oxidation process reduction, showing that for the Ti-6Al-4V alloy, the lifetime is affected strongly by the laser treatment with an increase in this superficial protection.
Structure, Texture and Tensile Properties of Ti6Al4V Produced by Selective Laser Melting
Production Engineering Archives, 2019
Additive manufacturing has recently expanded its potential with the development of selective laser melting (SLM) of metallic powders. This study investigates the relation between the mechanical properties and the microstructure of Ti6Al4V alloy produced by SLM followed by a hot isostatic pressing (HIP) treatment. HIP treatment minimizes the detrimental influence of material defects. Tensile specimens produced with reference to specific building axes were prepared using a Renishaw A250 system. It has been found that the tensile strength and elongation depend on specimen building direction. Microstructural and textural characterizations were carried out to identify the source of differences.
Materials Testing, 2023
Selective laser melting is a production method that results in a large amount of residual stress due to high cooling rates and high thermal gradients. Although there are many studies examining the effects of process parameters on residual stress or mechanical properties in the literature, there are a few studies investigating the effects of changing laser power and scanning velocity (exposure time) at constant energy density on residual stress or mechanical properties and these studies have different results. This is a comprehensive study in this field that includes detailed comparisons with the results of similar studies in the literature. In this study, firstly specimens were produced at different process parameters and it was tried to find the process parameters that will obtain the highest relative density among the trials. Then at the constant energy density (85.0 J mm −3), which the maximum density has been obtained the effects of changing laser power and scanning velocity on residual stress, mechanical properties, microstructure and relative density were investigated. It was observed that at constant energy density, increasing or decreasing laser power and scanning velocity did not increase or decrease residual stress, tensile strength, % elongation and relative density monotonously.
Rapid Prototyping Journal, 2020
Purpose Melting, fusion and solidification are the principal mechanisms used in selective laser melting to produce a product. Several thermal phenomena occur during the fabrication process, such as powder melting, melt pool formation, mixing of materials (fusion), rapid solidification, re-melting, high thermal gradient, reheating and cooling. These phenomena result in several types of pores, defects, irregular surfaces, bending and residual stress. This paper aims to focus on the physical behaviors of Ti-6Al-4V alloy at several scanning speeds and their effect on porosity and metallurgical properties. Design/methodology/approach Seven scanning speeds between 150 and 1000 mm/s were chosen to observe the occurrence of different pores, defects and microstructural formations and their effect on hardness and tensile properties. Findings The various mentioned malformations occur due to the results of possible uncertainties during the melting-fusion-solidification process. Size, shape, nu...
The tensile properties, mode I fracture toughness (K Ic), fatigue crack growth behavior, and unnotched fatigue strength of additively manufactured Ti-6Al-4V (Ti64) alloy using selective laser melting (SLM) technique were investigated. Four different combinations of layer thickness (t)-scan rotation between successive layers (f), which resulted in mesostructures that range from through-thickness columnar prior b grains with square cross-sections, whose side lengths equal to the scan spacing, to near-equiaxed mesostructures in both build and transverse directions, were explored. Possible anisotropy in mechanical properties was investigated by conducting tests on samples whose loading axis is either parallel or perpendicular to the build directions. In all cases, the microstructure consisted of fine a/a 0 lath structure, where a 0 is the metastable martensitic Ti phase that is acicular in shape, within the prior b grains. Experimental results show that the process parameter combinations of t ¼ 60 mm and f ¼ 67 results in an alloy that exhibits high yield strength (>1100 MPa) and ductility (>12%) simultaneously, K Ic of 58 MPa ffiffiffiffiffiffi m p , and unnotched fatigue strength, which is similar to that of the same alloy but manufactured using conventional techniques. The anisotropy in properties, overall, was found to be not substantial, even in the case where columnar growth of prior b grains occurs in the build direction. The values of the Paris exponents for steady state fatigue crack growth (FCG) are much lower than those reported for conventionally manufactured Ti64, suggesting higher FCG resistance in SLM Ti64. Analysis of the effective microstructural length scale that controls the near-threshold FCG rate suggests that it is the colony size that dominates this behavior. Overall, the results of this study indicate directions for process parameter optimization that would lead to SLM Ti64 that is not only has high strength, but also is damage tolerant.