Ti-13Nb-13Zr alloy is an orthopedic implant material possessing good mechanical properties, corrosion resistance, and biocompatibility. An international standard suggests a heat treatment known as ...“capability aging” for this alloy. This study provides extensive data of mechanical properties under a wide temperature condition built around the capability-aging process. Specifically, it investigates the effect of annealing temperature (573–973 K) on mechanical properties (i.e., yield strength, tensile strength, hardness, Young’s modulus, and mechanical compatibility) of Ti-13Nb-13Zr alloys. Although these mechanical properties showed similar trends with respect to the annealing temperature, Young’s modulus exhibited the highest value at 873 K in contrast to those of the other properties shown at 773 K. Such a disparity was discussed in light of static spheroidization and phase decomposition based on microstructural characteristics of the annealed Ti-13Nb-13Zr alloys.
Electrically-assisted (EA) deformation has shown promising effects in increasing formability and reducing springback in sheet metal forming. This work experimentally and analytically investigated the ...influence of non-uniform and transient Joule heating on the plastic flow stress of titanium which evolved nonlinearity with time and deformation. Three-stage constitutive analysis was carried out in the present study. First, the pure influence of non-uniform Joule heating was investigated in terms of linear elastic thermal expansion, which then explained the measured drops in stress. Second, the Johnson-Cook model was adopted to interpret a plastic thermal-mechanical behavior of the material loaded at a constant quasi-static deformation rate under the uniaxial tension combined with a single pulse of electric current. Finally, it was revealed that the sudden change in strain rate and rapid heating rate due to an electric current pulse could give rise to the transient occurrence of dynamic strain aging (DSA) in materials. This resulted in an accumulated plastic strain as well as transient high-temperature strain hardening, which estimated the experimentally measured data well. The DSA contribution revealed in this work could help to explain many observations in the past studies in the field of EA deformation.
•The model incorporates the non-uniform Joule heating.•Modeled the response from a single electrical pulse, paved the foundation for future multi-pulse cases.•Dynamic strain aging due to rapid change in strain rate and heating rate in the case of single-pulse case is modeled.•Fine experimental measurement of strain change in the single-pulse case is presented.
Directed energy deposited (DED) Ti–6Al–4V components and prototypes are quickly growing in prevalence in aerospace and biomedical industries for their increased strength and fast processing time. ...However, one of the remaining challenges in DED processes, particularly laser engineered net shaping (LENS), is the characterization of the inherent anisotropy in material properties. Anisotropy in microstructure, porosity and mechanical behavior arises due to unique material thermal histories during processing. Understanding anisotropy in additive manufacturing can lead to refined process parameters, characterization methods, material and thermal modeling as well as improved mechanical properties. This paper investigates the anisotropic mechanical properties, specifically ultimate tensile strength, of LENS-processed Ti–6Al–4V and how these properties depend on geometry and direction of build processing. Mechanical properties were found to be most desirable when the tensile orientation is orthogonal to the build direction and parallel to the scan direction as well as closer to the center of a fully dense component. This study investigates microstructure through X-ray diffraction, fractography and porosity shape and connectivity analysis. Models that predict mechanical behavior based on processing details are in development. There is potential to achieve desirable mechanical properties through melt pool and thermal controls for high-strength and energy efficient materials by predicting mechanical properties from process parameters.
The hydrogen embrittlement (HE) resistance of a fine-grained equiatomic CoCrFeNi high-entropy alloy (HEA) is investigated via tensile testing under electrochemical H charging. The HE behavior is ...compared with that of HEA specimens charged with 100 MPa of H gas. The fine-grained HEA shows > 40% elongation with a tensile strength of ~800 MPa under electrochemical H charging. Meanwhile, H gas-charged specimens with a uniform distribution of H show deformation twin-related intergranular cracks, whose initiation length decreases owing to grain refinement. Such small cracks, which feature blunted tips, do not significantly affect the fracture of the specimens. The electrochemically H-charged specimens exhibit numerous surface cracks because of their higher surface H content compared with that of the H gas-charged specimens. Nevertheless, similar to the case of the H gas-charged specimens, most of the cracks do not propagate significantly. In conclusion, fine-grained HEA exhibits remarkable resistance to H-related crack growth.
In this study, the ideal alloying element (among Cr, V, and Mo carbides) to enhance the resistance to hydrogen embrittlement (HE) in a tempered martensitic steel was investigated. Four types of ...steels were designed to contain cementites, Cr-rich M
C
carbides, V carbides, and Mo carbides, respectively. These steels were tailored to possess a comparable tensile strength (~1.6 GPa). The HE resistances of these steels were evaluated through the slow strain rate test and cyclic corrosion test. The results showed an enhanced HE resistance, characterized by a high notch fracture strength after hydrogen charging, in the samples containing V carbides and Mo carbides. In particular, Mo carbide was regarded as the most ideal alloying element for HE resistance because of the high resistivity parameter, inhibited hydrogen penetration, and suppressed strength loss by internal hydrogen.
The mechanical properties and microstructure were investigated under different Zn content and heat treatment conditions in a Mg–Zn–Y–Gd cast alloy. A part of the long period stacking order (LPSO) ...phases transformed to W-Mg3Zn3RE2 phases with an increase in Zn content from 0.9 at.% to 1.8 at.%, and the ultimate tensile strength (UTS) increased from 229 MPa to 248 MPa. With solution treatment at 480 °C, the content of the LPSO phase and strength sharply decreased in the Mg-1.8Zn-0.8Y-0.8Gd alloy, whereas this change was not significantly observed in the Mg–0.9Zn–0.8Y–0.8Gd alloy. After solution treatment, the elongation significantly improved and the UTS sharply decreased in both alloys. The lamellar and filminess LPSO phases were observed with aging treatment at 200 °C. Moreover, the strengthening efficiency of lamellar and filminess LPSO phases was lower than that of the block LPSO phases. Therefore, the UTS of the T6 state was lower than that of the as-cast alloy.
► A twinning-induced plasticity steel showed degradation of uniform elongation by decreasing deformation temperature. ► Intergranular and ε/α′ boundary cracking, and fracture associated with ...ε-martensite were observed at 123K. ► The cryogenic tensile properties were improved with decreasing grain size. ► One of the important reasons of the improvement was clarified to be suppression of formation of ε-martensite.
Cryogenic mechanical properties of twinning-induced plasticity steels of various grain sizes were investigated by the tensile tests. Specimens with coarse grain sizes, e.g. 10, 23 and 37μm, showed a brittle fracture at 123K. The embrittlement was suppressed by a grain refinement to 3.5μm by cold rolling and recrystallization. Furthermore, a grain refinement to 460nm by warm caliber rolling suppressed the embrittlement more effectively compared with the grain refinement via cold rolling and recrystallization treatment. The grain refinements improved the tensile elongation, yield strength, and ultimate tensile strength significantly at 123K. It was found that the suppression of the embrittlement was caused by the reductions in the amount of ε-martensite.
A high-Mn austenitic steel represents excellent combination of tensile strength and ductility, but shows very low yield strength. To increase the yield strength, pre-deformation is applied before ...use. However, the other properties such as fatigue resistance should also remain high. In this study the influence of pre-strain on tensile and low cycle fatigue (LCF) resistance were investigated. The amount of pre-strain (ε=0, 0.2 and 0.4) and pre-straining temperature (203K∼490K) were varied, which resulted in the variation of deformation-induced twin boundaries and fraction of martensite. Tensile tests and fully-reversed strain-controlled fatigue tests were conducted on plate-type samples. As the amount of pre-strain increased, yield and tensile strength were increased, but ductility and LCF life were decreased. The LCF properties of samples at a fixed amount of pre-strain were analyzed in the context of the fractions of martensite and mechanical twin boundaries. The presence of a small amount of ε-martensite increased yield stress and fatigue resistance by fostering deflected-and-branched propagation of fatigue cracks, whereas a high fraction of ε-martensite degraded the mechanical properties. In contrast, the presence of a high fraction of mechanical twin boundaries enhanced both tensile and fatigue properties under the conditions used in this work. The sizes of dislocation cells decreased and spacing of fatigue striations narrowed as the fraction of mechanical twin boundaries increased. Results suggest that a microstructure composed of ~20% ε-martensite and numerous mechanical twin boundaries can represent superior tensile and fatigue properties; this microstructure was obtained by step pre-straining (SP) process, where pre-strain was imposed twice at different temperatures.
In this study, Ti–20Zr–(8–12)Nb–3Sn (at.%) shape memory alloys were fabricated by arc melting method and their phase constitutions, texture characteristics and superelastic behaviors were ...investigated by X-ray diffraction (XRD), electron back-scattered diffraction (EBSD) and tensile tests. Main α" martensite and minor β were formed in solution-treated Ti–20Zr–8Nb–3Sn specimen. With increasing Nb content to above 10 at.%, only the β phase was observed. The texture characteristics of these solution-treated Ti–Zr–Nb–Sn alloys were found to be tuned by varying Nb content. A highly dominant {001}β < 110>β recrystallization texture was evolved to dominant Goss texture ((110)β001β) and weak γ-fiber texture ((111)β//rolling plane) with increasing Nb content from 9 to 12 at.%. The Goss texture has not previously been reported in Ti–Zr–Nb–Sn alloys. The texture evolutions of the present Ti–Zr–Nb–Sn alloys were related to the strong β-stabilizing effect of Nb. Dominant shape memory effect was observed in Ti–20Zr–(9, 10)Nb–3Sn specimens and room temperature superelasticity was observed in Ti–20Zr–(11, 12)Nb–3Sn specimens. Compared with the Ti–20Zr–12Nb–3Sn specimen, the Ti–20Zr–11Nb–3Sn specimen exhibited superior superelasticity. The simultaneous presence of {001}β < 110>β texture, Goss texture and room temperature superelasticity in the Ti–20Zr–11Nb–3Sn specimen is beneficial to the practical biomedical application.
•This study has expanded a method of rapidly solidified flaky powder metallurgy (RS FP/M) to AZ91 alloy.•RS FP/M AZ91 accomplishes the high strain-rate superplasticity (HSRS) at 623 K.•The achieved ...HSRS arises from an effective grain refinement and thermal stability by RS FP/M technique.
In this study, the authors successfully obtained high strain-rate superplasticity (HSRS) for an AZ91 Mg alloy using rapidly solidified flaky powder metallurgy (RS FP/M). The RS FP/M AZ91 shows an elongation to failure of 465% at a temperature and initial strain rate of 623 K and 10−2 s−1, respectively. Furthermore, the optimum superplastic strain rate for the maximum elongation was 10−2 s−1, which is higher than those attained by other methods. The HSRS obtained in this study is attributed to an effective grain refinement (∼1 μm) and high thermal stability. The bimodal grain structure may further contribute to HSRS.
PDF
