Effects of Laser Surface Melting on Ti 30Nb 2Sn Sintered Alloy

[EN] Laser surface melting (LSM) is used to simultaneously melt a thin layer and quench Ti¿30Nb¿2Sn substrate produced by powder metallurgy route. Results show LSM is useful to eliminate non-desirable open porosity and to reduce even more the Young Modulus. The best microstructure is achieved below the melting pool where high peak temperature combined with high cooling rate during laser processing is present. LSM retains beta titanium without traces of martensite or grain boundary alpha due to oxygen contamination.This work is financially supported by Spanish Ministry of Science (Grant No. MAT2011-28492-C03-01 and BES-2009-013589) and PIB2010BZ-00448 International project.Candel Bou, JJ.; Amado, JM.; Amigó, V.; Tobar, MJ. (2017). Effects of Laser Surface Melting on Ti 30Nb 2Sn Sintered Alloy. Advanced Engineering Materials. 19(6):1500640-1-1500640-4. doi:10.1002/adem.201500640S1500640-11500640-419

Electropolishing of laser powder bed-fused IN625 components in an ionic electrolyte

This work presents the first practical application of ionic electrolytes for electropolishing of nickel-based superalloys. It contains the results of an experiment-driven optimization of the applied potential and electrolyte temperature during electropolishing of laser powder bed-fused IN625 components containing surfaces oriented to the building platform under angles varying from 0 to 135°. For comparative purposes, the roughness profilometry and confocal microscopy techniques were used to characterize the surface finish topographies and the material removal rates of IN625 components subjected to electropolishing in ionic and acidic (reference) electrolytes. After 4 h of electropolishing in both electrolytes, a roughness of Ra ≤ 6.3 μm (ISO N9 grade number of roughness) was obtained for all the build orientations. To elaborate, both electrolytes manifested identical roughness evolutions with time on the 45° (75% Ra reduction) and 90°-oriented (65% Ra reduction) surfaces. Although the roughness reduction on the 135°-oriented surface in the ionic electrolyte was 17% less than in the acidic electrolyte, the former provided a more uniform roughness profile on the 0°-oriented surface (30% Ra reduction) and 44% higher current efficiency than the acidic electrolyte. This work proves that ionic electrolytes constitute a greener alternative to industrial acidic mixtures for electropolishing of three-dimensional (3D)-printed parts from nickel-based superalloys

Temperature- and time-dependent mechanical behavior of post-treated IN625 alloy processed by laser powder bed fusion

The microstructure and mechanical properties of IN625 alloy processed by laser powder bed fusion (LPBF) and then subjected to stress relief annealing, high temperature solution treatment, and hot isostatic pressing were studied. Tensile testing to failure was carried out in the 25–871 °C temperature range. Creep testing was conducted at 760 °C under 0.5–0.9 yield stress conditions. The results of the present study provided valuable insights into the static and creep properties of LPBF IN625 alloy, as compared to a wrought annealed alloy of similar composition. It was shown that at temperatures below 538 °C, the mechanical resistance and elongation to failure of the LPBF alloy were similar to those of its wrought counterpart, whereas at higher temperatures, the elongation to failure of the LPBF alloy became significantly lower than that of the wrought alloy. The solution-treated LPBF alloy exhibited significantly improved creep properties at 760 °C as compared to the wrought annealed alloy, especially under intermediate and low levels of stress

Microstructural and Microhardness Evolution from Homogenization and Hot Isostatic Pressing on Selective Laser Melted Inconel 718: Structure, Texture, and Phases

In this work, the microstructure, texture, phases, and microhardness of 45° printed (with respect to the build direction) homogenized, and hot isostatically pressed (HIP) cylindrical IN718 specimens are investigated. Phase morphology, grain size, microhardness, and crystallographic texture at the bottom of each specimen differ from those of the top due to changes in cooling rate. High cooling rates during the printing process generated a columnar grain structure parallel to the building direction in the as-printed condition with a texture transition from (001) orientation at the bottom of the specimen to (111) orientation towards the specimen top based on EBSD analysis. A mixed columnar and equiaxed grain structure associated with about a 15% reduction in texture is achieved after homogenization treatment. HIP treatment caused significant grain coarsening, and engendered equiaxed grains with an average diameter of 154.8 µm. These treatments promoted the growth of δ-phase (Ni3Nb) and MC-type brittle (Ti, Nb)C carbides at grain boundaries. Laves phase (Fe2Nb) was also observed in the as-printed and homogenized specimens. Ostwald ripening of (Ti, Nb)C carbides caused excessive grain growth at the bottom of the HIPed IN718 specimens, while smaller grains were observed at their top. Microhardness in the as-fabricated specimens was 236.9 HV and increased in the homogenized specimens by 19.3% to 282.6 HV due to more even distribution of secondary precipitates, and the nucleation of smaller grains. A 36.1% reduction in microhardness to 180.5 HV was found in the HIPed condition due to phase dissolution and differences in grain morphology

Reflection of an ultrasonic wave on the bone-implant interface: Effect of the roughness parameters

Quantitative ultrasound can be used to characterize the evolution of the bone-implant interface (BII), which is a complex system due to the implant surface roughness and to partial contact between bone and the implant. The aim of this study is to derive the main determinants of the ultrasonic response of the BII during osseointegration phenomena. The influence of (i) the surface roughness parameters and (ii) the thickness W of a soft tissue layer on the reflection coefficient r of the BII was investigated using a two-dimensional finite element model. When W increases from 0 to 150 μm, r increases from values in the range [0.45; 0.55] to values in the range [0.75; 0.88] according to the roughness parameters. An optimization method was developed to determine the sinusoidal roughness profile leading to the most similar ultrasonic response for all values of W compared to the original profile. The results show that the difference between the ultrasonic responses of the optimal sinusoidal profile and of the original profile was lower to typical experimental errors. This approach provides a better understanding of the ultrasonic response of the BII, which may be used in future numerical simulation realized at the scale of an implant

Structure, Texture and Phases in 3D Printed IN718 Alloy Subjected to Homogenization and HIP Treatments

3D printing results in anisotropy in the microstructure and mechanical properties. The focus of this study is to investigate the structure, texture and phase evolution of the as-printed and heat treated IN718 superalloy. Cylindrical specimens, printed by powder-bed additive manufacturing technique, were subjected to two post-treatments: homogenization (1100 °C, 1 h, furnace cooling) and hot isostatic pressing (HIP) (1160 °C, 100 MPa, 4 h, furnace cooling). The Selective laser melting (SLM) printed microstructure exhibited a columnar architecture, parallel to the building direction, due to the heat flow towards negative z-direction. Whereas, a unique structural morphology was observed in the x-y plane due to different cooling rates resulting from laser beam overlapping. Post-processing treatments reorganized the columnar structure of a strong {002} texture into fine columnar and/or equiaxed grains of random orientations. Equiaxed structure of about 150 µm average grain size, was achieved after homogenization and HIP treatments. Both δ-phase and MC-type brittle carbides, having rough morphologies, were formed at the grain boundaries. Delta-phase formed due to γ″-phase dissolution in the γ matrix, while MC-type carbides nucleates grew by diffusion of solute atoms. The presence of (Nb0.78Ti0.22)C carbide phase, with an fcc structure having a lattice parameter a = 4.43 Å, was revealed using Energy dispersive spectrometer (EDS) and X-ray diffractometer (XRD) analysis. The solidification behavior of IN718 alloy was described to elucidate the evolution of different phases during selective laser melting and post-processing heat treatments of IN71

Влияние комбинации радиально-сдвиговой прокатки и ротационной ковки на напряженно-деформированное состояние прутковой заготовки малого диаметра из титановых сплавов

The paper focuses on the finite element method used to simulate the stress-strain state of a small-diameter bar stock during hot-forming in a combination of radial shear rolling (RSR) and rotary forging (RF). Simulation was carried out using the rheological model of the Ti-6Al-4V titanium-based alloy with the QForm VX software. A combination of radial shear rolling of a workpiece with a diameter of 15 mm to 12 mm bar in one pass and subsequent rotary forging in one, two and three passes to obtain bars with diameters 11, 10 and 8 mm is simulated. During the simulation, step-by-step accumulation of plastic deformation was taken into account in the conditions of its nonuniform distribution. The intermediate and finite fields of plastic deformation, strain rate and average stress are obtained. It is shown that plastic deformation distribution after RSR has an expressed gradient with a maximum value (3 or more) at the periphery of the cross-section and a minimum value (about 1) at the center. As a result of RF, even with small reductions, the stress-strain state becomes much more uniform compared with a workpiece of the same diameter after radial shear rolling only. In addition, residual tensile stresses due to compressive stresses during rotary forging are reduced. Direct experimental testing of the combined deformation method was carried out for a promising medical-grade Ti-Zr-Nb shape memory alloy when manufacturing 7-8 mm diameter rods in experimental production conditions. Qualitative confirmation of modeling results is obtained by metallographic analysis. It is shown that the combination of radial shear rolling and rotary forging is promising for creating industrial technologies for the manufacture of small-diameter rods with a highly uniform finely-dispersed structure.Работа посвящена конечно-элементному моделированию напряженно-деформированного состояния прутковой заготовки малого диаметра при горячей обработке давлением в комбинации радиально-сдвиговой прокатки (РСП) и ротационной ковки (РК). Моделирование выполнено с использованием реологической модели титанового сплава Ti—6Al—4V с помощью программы QForm VX. Смоделировано сочетание радиально-сдвиговой прокатки за 1 проход заготовки диаметром 15 мм на пруток диаметром 12 мм и последующей ротационной ковки в 1, 2 и 3 прохода с получением прутков диаметрами 11, 10 и 8 мм. Учитывалось пооперационное накопление пластической деформации в условиях неравномерности ее распределения. Получены промежуточные и конечные поля пластической деформации, скорости деформации и среднего напряжения. Показано, что распределение пластической деформации после РСП имеет выраженную градиентность с максимальным значением (3 и более) на периферии сечения и минимальным (около 1) в центре. В результате РК даже с небольшими обжатиями напряженно-деформированное состояние становится существенно более однородным по сравнению с заготовкой такого же диаметра только после радиально-сдвиговой прокатки. Кроме того, уменьшаются остаточные напряжения растяжения из-за сжимающих напряжений при ротационной ковке. Прямое экспериментальное опробование комбинированного способа деформации проведено для перспективного сплава Ti—Zr—Nb с памятью формы медицинского назначения при изготовлении прутков диаметром 7—8 мм в условиях опытно-промышленного производства. Получено качественное подтверждение результатов моделирования металлографическим анализом. Показана перспективность сочетания радиально-сдвиговой прокатки и ротационной ковки для создания индустриальных технологий изготовления прутков малого диаметра с высокой однородностью мелкодисперсной структуры