Formation of alpha phase via pseudospinodal decomposition in Ti-Nb-Fe based alloys

Herein, the fine-scaled α phase precipitation during step-quench heat treatments in Ti‐15Nb‐3.0Fe and Ti‐11Nb‐3.5Fe (wt%) alloys was evaluated. Thermodynamic analyses suggest that Ti‐11Nb‐3.5Fe alloy should present homogenous α phase formation via the pseudospinodal mechanism when solution-treated and step-quenched at 450 °C, which is confirmed in this work. STEM-EDX measurements confirm the non-equilibrium state of the α phase precipitates, whose Nb content is significantly higher than that of the α phase laths obtained after solution heat treatment followed by furnace cooling. Fe seems to play an important role in the precipitation mechanism, and is depleted from α phase laths in a short aging time189201205FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP2014/24449-0; 2014/06099-1This work was supported by FAPESP (grants numbers 2014/24449-0 and 2014/06099-1). The authors acknowledge the Brazilian Nanotechnology National Laboratory (LNNano) at CNPEM, Brazi

Orthorhombic martensite formation upon aging in a Ti-30Nb-4Sn alloy

The characteristics of orthorhombic martensite (α″) formed by step-quenching in a Ti-30Nb-4Sn (wt%) alloy have been investigated by transmission electron microscopy (TEM) and X-ray diffraction (XRD). According to literature, α″ lattice parameters depend mainly on the composition of the parent β phase. In this study, samples subjected to step quenching heat treatment presented α″ phase formation in the proximity of α phase laths, driven by two combined factors: solute rejection and lattice strain. Our results indicate that as the aging is prolonged, α″ becomes richer in solute content, which makes it more similar to the parent β phase. An average 2.55% lattice strain along [110]β directions was found to be necessary in order to obtain α″ from the β phase after 24 h of aging at 400 °C, followed by water-quenching. The initial lattice strain along the same direction was estimated at approximately 3.60% with zero aging time. The precipitation of the α phase does not inhibit a solute rich α″ phase formation183238246CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQFUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP484379/2012-72012/10164-8; 2013/50391-6The authors gratefully acknowledge the Brazilian research funding agencies FAPESP (#2012/10164-8 and #2013/50391-6) and CNPq (#484379/2012-7) for their financial support; Companhia Brasileira de Metalurgia e Mineração (CBMM) for the Niobium supplied and also the Brazilian Nanotechnology National Laboratory (LME/LNNano/CNPEM) and OSU (The Ohio State University) for the use of electron microscopy facilities and the technical support during the TEM wor

Effects of Sn addition on the microstructure, mechanical properties and corrosion behavior of Ti–Nb–Sn alloys

Ti and Ti alloys are widely used in restorative surgery because of their good biocompatibility, enhanced mechanical behavior and high corrosion resistance in physiological media. The corrosion resistance of Ti-based materials is due to the spontaneous formation of the TiO2 oxide film on their surface, which exhibits elevated stability in biological fluids. Ti–Nb alloys, depending on the composition and the processing routes to which the alloys are subjected, have high mechanical strength combined with low elastic modulus. The addition of Sn to Ti–Nb alloys allows the phase transformations to be controlled, particularly the precipitation of ω phase. The aim of this study is to discuss the microstructure, mechanical properties and corrosion behavior of cast Ti–Nb alloys to which Sn has been added. Samples were centrifugally cast in a copper mold, and the microstructure was characterized using optical microscopy, scanning electron microscopy and X-ray diffractometry. Mechanical behavior evaluation was performed using Berkovich nanoindentation, Vickers hardness and compression tests. The corrosion behavior was evaluated in Ringer's solution at room temperature using electrochemical techniques. The results obtained suggested that the physical, mechanical and chemical behaviors of the Ti–Nb–Sn alloys are directly dependent on the Sn content96273281CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQFUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP484379/2012-72011/23942-6The authors gratefully acknowledge the Brazilian research funding agencies FAPESP (State of São Paulo Research Foundation) Grant # 2011/23942-6, CNPq Grant # 484379/2012-7 (National Council for Scientific and Technological Development) and CAPES (Federal Agency for the Support and Evaluation of Graduate Education) for their financial support of this wor

Solute lean ti-nb-fe alloys : an exploratory study

In this study, we explored the Ti-Nb-Fe system to find an optimal cost-effective composition with the lowest elastic modulus and the lowest added Nb content. Six Ti-(31-4x)Nb-(1+0.5x)Fe ingots were prepared and Nb was substituted with Fe, starting at Ti-31Nb-1.0Fe and going up to Ti-11Nb-3.5Fe (wt%). The ingots were subjected to cold rolling, recrystallization and solution treatment, followed by water-quenching (WQ), furnace cooling (FC) or step-quenching to 350 °C, which caused massive formation of isothermal ω phase. All the water-quenched alloys displayed athermal ω phase, which is apparently the result of fully collapsed β phase. The Fe content improved the compressive strength of the alloys. In the FC alloys, substitution with Fe favored the formation of α phase instead of ω phase, giving rise to a solute-rich β phase with a lattice parameter of 0.3249 nm. Among the FC alloys, the lowest modulus of 83±4 GPa was obtained in the Ti-19Nb-2.5Fe alloy, which exhibited fine and well dispersed α precipitation and absence of ω phase. DSC experiments indicated that the experimental alloys showed varying phase stability during heating65761769FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP2014/24449-0; 2014/06099-1This research was funded by FAPESP (São Paulo State Research Foundation) through Grants 2014/24449-0 and 2014/06099-1. All the microscopy work was carried out at the LNNano/CNPEM facilities. The authors thank the company CBMM for supplying the niobium used in this wor

α phase precipitation and mechanical properties of Nb-modified Ti-5553 alloy

Metastable β Ti alloys can be strengthened by controlling α phase precipitation during aging heat treatments. An example of this is Ti-5553 alloy (Ti-5Al-5Mo-5V–3Cr-0.5Fe wt%), which has been extensively applied in the aerospace industry due to its high strength-to-weight ratio. The substitution of V with Nb in Ti-5553 enhances the alloy's hardenability and may alter the mechanisms of α phase precipitation, thereby affecting its mechanical properties. Accordingly, the aim of this study was to evaluate the α phase precipitation and mechanical behavior of Nb-modified Ti-5553. Samples were prepared by arc melting and hot working by swaging, and then subjected to HT1 (solution heat-treated above β transus and aged at 600 °C for 600 min) or HT2 (heat-treated at temperatures below β transus, air cooled, heated to 600 °C and aged for 600 min). Compared to the base Ti-5553, the Nb-modified alloy exhibited improved mechanical strength in the HT1 condition due to nonhomogeneous α phase precipitation, but lower ductility in both aging conditions. An examination of the fracture surface revealed that the substitution of V with Nb did not change the fracture behavior and all the samples showed a quasi-cleavage fracture mode with some evidence of intergranular features. The Ti-5553 samples subjected to HT1 presented more dimples and hence, higher ductility. On the other hand, the HT2 samples showed fracture surfaces with predominantly transgranular features. Lastly, with regard to the pseudospinodal mechanism in the Nb-modified alloy, it was found that the substitution of V with Nb reduces the temperature at which pseudospinodal decomposition occurs by roughly 75 °C670112121CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQFUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESPNão temNão temThe authors gratefully acknowledge the Brazilian research funding agencies FAPESP (São Paulo Research Foundation) and CNPq (National Council for Scientific and Technological Development) for their financial support, CBMM Co. for supplying Nb, and Prof. Hamish L. Fraser for the use of the FIB/TEM facilities at CEMAS/Ohio State Universit

Assessment of laser power and scan speed influence on microstructural features and consolidation of AISI H13 tool steel processed by additive manufacturing

Additive manufacturing can produce parts with complex geometries in fewer steps than conventional processing, which leads to cost reduction and a higher quality of goods. One potential application is the production of molds and dies with conformal cooling for injection molding, die casting, and forging. AISI H13 tool steel is typically used in these applications because of its high hardness at elevated temperatures, high wear resistance, and good toughness. However, available data on the processing of H13 steel by additive manufacturing are still scarce. Thus, this study focused on the processability of H13 tool steel by powder bed fusion and its microstructural characterization. Laser power (97−216 W) and scan speed (300−700 mm/s) were varied, and the consolidation of parts, common defects, solidification structure, microstructure, and hardness were evaluated. Over the range of processing parameters, microstructural features were mostly identical, consisting of a predominantly cellular solidification structure of martensite and 19.8 %–25.9 % of retained austenite. Cellular/dendritic solidification structure displayed C, Cr, and V segregation toward cell walls. The thermal cycle resulted in alternating layers of heat-affected zones, which varied somewhat in hardness and microstructure. Retained austenite was correlated to the solidification structure and displayed a preferential orientation with {001}//build direction. Density and porosity maps were obtained by helium gas pycnometry and light optical microscopy, respectively, and, along with linear crack density, were used to determine appropriate processing parameters for H13 tool steel. Thermal diffusivity, thermal conductivity, and thermal capacity were measured to determine dimensionless processing parameters, which were then compared to others reported in the literature3