Search

The mechanical behavior of commercial purity Ti (CP-Ti)/Ti–6Al–2Zr–1Mo–1V structurally graded materials (SGMs) fabricated by laser additive manufacturing was investigated via uniaxial tensile experiments. Although the strength of all SGM specimens is higher than that of the monolithic CP-Ti specimens, only the SGM specimen of Ø10mm gauge diameter with bulky α-grains exhibits excellent plasticity comparable to the CP-Ti specimen under the same conditions. The SGM presents a potential for use as load-bearing components due to its good strength–ductility balance. [ABSTRACT FROM AUTHOR]

Abstract Under high strain rate loadings, many engineering materials exhibit quite different deformation behavior from those under quasi-static loadings, and adiabatic shear band (ASB) is normally generated with degradation of material property. In this study, the deformation response of LAMed Ti-6.5Al-3.5Mo-1.5Zr-0.3Si titanium alloy (TC11) under high strain rates (2800s−1 and 2900s−1) is investigated for both as-deposited state and heat-treated state (annealed at 1263 K for 1 h followed by annealed at 803 K for 6 h) by using the split Hopkinson pressure bar (SHPB). Results indicate that the as-deposited alloy has a unique mixed grain morphology (coarse columnar grains and fine equiaxed grains) with ultrafine basket-weave microstructure. Under high strain rate loadings, the as-deposited alloy possesses excellent yield strength but with poor plasticity and high adiabatic shear susceptibility. After heat treatment, the yield strength of alloy is sacrificed due to the reduced contents of ultrafine α lamellas, but the partially globularization of continuous grain boundary α phases greatly improves the plasticity of alloy that the adiabatic shear susceptibility is efficiently suppressed. Highlights • TC11 titanium alloy plate was fabricated by laser additive manufacture technology. • High strain rate response of the prepared alloy was investigated. • Dynamic mechanical properties corresponding to different microstructures are given. • Heat treatment efficiently suppress the adiabatic shear susceptibility of alloy. [ABSTRACT FROM AUTHOR]

Good hydrogen-environmentally embrittlement (HEE) resistance is necessary for safe service of critical main load-bearing ultra-high strength steel (UHSS) components of advanced aircrafts in marine atmosphere environment. Controlling isothermal tempering time is one important heat treatment method to optimize HEE resistance of UHSS by designing microstructure. Influence of isothermal tempering time at 482 °C on microstructures and HEE susceptibilities of laser additively manufactured (LAM) AerMet100 steel was investigated by several material characterization methods and slow strain rate tensile (SSRT) tests in both of air and 3.5 wt% NaCl aqueous solution. Results mainly indicate that microstructure evolution behaviors of LAM AerMet100 steel successively include martensite and retained austenite decomposition, M 2 C carbide formation and coarsening, and film-like reverted austenite formation and thickening. Short-time tempering specimens of LAM AerMet100 steel has the highest strength-loss-index in all of the specimens due to the lowest austenite amount. The lower HEE susceptibility of LAM AerMet100 steel in long-time tempering condition is mainly corresponding to M 2 C carbide coarsening and film-like reverted austenite thickening. Furthermore, difference of hydrogen charging method strongly influences macro-fracture behaviors of the SSRT specimens, but micro-cracking modes of the steel in different conditions are predominantly martensite packet/plate boundary cracking. Under open-circuit potential condition, HEE cracking zone is prone to be origin from pitting corrosion sites, and the SSRT specimen in long-time tempering condition have a good ductility; in contrast, under cathodic polarization condition, HEE cracking zone is around the circumferential zones, and the tensile specimens are brittle fracture. These findings are important when considering achieving improved HEE resistance for LAM AerMet100 steel tempered at 482 °C of a longer isothermal tempering time at the strength level of interest. [ABSTRACT FROM AUTHOR]

Ultrahigh-strength AerMet100 steel plate was fabricated by laser additive manufacturing process (LAM) followed by subsequent heat treatments. Microstructures and tensile mechanical properties of the steel were examined using optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and universal mechanical testing machine. The results indicate that post-LAM heat treatments greatly change alloy carbide characteristics, decrease austenite content and prompt the formation of fine equiaxed prior-austenite grains for LAM AerMet100 steel. Compared to fine short rod-like Nb-rich MC carbides and needle-like M 3 C carbides in as-deposited specimens, alloy carbides in tempered specimens have the large changes, which include fine spherical Nb-rich MC carbides, fine rod-like M 2 C carbides, large-size spherical Mo-rich M 6 C carbides and Cr-rich M 23 C 6 carbides. And the fine rod-like M 2 C carbides are dispersive distribution and coherency with the martix martensite, resulting in strong coherent strain strengthening. After proper post homogeneity heat treatment processes, tensile mechanical properties of LAM AerMet100 steel have the comprehensive improvement, which are comparable to those of the forged ones. In comparison with low ductility of as-deposited specimen, the higher ductility of tempered specimen is mainly related to its extremely strong strain-strengthening capability achieved by dispersive precipitation of M 2 C carbides. With the increase of homogenization, the further improved ductility of tempered specimen mainly ascribe to the decreased amount and size of large-size alloy carbides (especially Mo-rich M 6 C carbide). [ABSTRACT FROM AUTHOR]

In order to evaluate the effects of microstructure characteristics on fatigue crack growth (FCG) resistance of laser additive manufactured (LAM) AerMet100 steel, microstructures and FCG behaviors (in Paris region) of as-deposited specimen and three types of tempered martensite specimens were examined. Results indicate as-deposited specimens of LAM AerMet100 steel have apparent texture characteristics of epitaxy unidirectional growth prior-austenite columnar grains and grain-interior inter-dendritic blocky retained austenite with [001] crystallographic orientation. And poor boundary cracking resistance of these texture characteristics along deposition direction mainly contributes to the FCG rate anisotropy of as-deposited specimens. After post-LAM heat treatments, the FCG resistance of all heat-treated specimens apparently improves with the fracture mode of transgranular cracking. With the increase of yield strength, the value of Paris coefficient C of the steel increases, but the value of Paris exponent m decreases. Compared to the poor dislocation slip resistance of bainite plates in as-deposited specimens, the improved dislocation slip resistance of martensite plates is mainly related to the strong dislocation pinning effect of fine dispersive rod-like coherent M 2 C carbides, resulting in the stronger FCG resistance of the heat-treated specimens. In the Paris region of low ΔK (< ~ 20 MPa m 1/2 ), fatigue cracks mainly propagate along the bainite (or martensite) plate interfaces, and the FCG rate of the steel can be effectively decreased by containing higher contents of thick film-like retained/reverted austenite; with the increase of Δ K , besides propagating along the soft inter-plate film-like austenite, fatigue cracks can also directly pass through the harder bainite (or martensite) plates with the striations and secondary cracks observed on fracture surfaces; in the Paris region of high Δ K (> ~ 70 MPa m 1/2 ), higher contents of retained/reverted austenite inversely accelerate the FCG rate of heat-treated LAM AerMet100 steel. In contrast, grain refinement has the little influence on the FCG rate (in most of Paris region) of the heat-treated specimens. [ABSTRACT FROM AUTHOR]

Highly-dense Al-5Si-1Cu-Mg alloy bulk was firstly produced by laser additive manufacture (LAM) technique. LAM involves extraordinary thermal cycles and will therefore significantly affect the microstructure. In this research, the phase evolution of LAMed Al-5Si-1Cu-Mg alloy was studied in detail by characterization along the deposition direction. The rapid solidification of LAM encourages the generation of various unstable phases of vermicular Si, fishbone shaped θ-Al 2 Cu, blocky π-Al 8 Mg 3 FeSi 6 and irregular Q-Al 5 Mg 8 Cu 2 Si 6 . As the increasing times of thermal cycling, phase evolution takes place by spheroidization of Si phases, transformation of π-Fe to plate-like β-Al 5 FeSi with dissolution of θ and Q phases. In particular, after certain times of thermal excursions, many micron-sized and nano-sized Q′ phases precipitate out from matrix, and the stabilized microstructure consists of α-Al, Q′, Si and β. [ABSTRACT FROM AUTHOR]

The control of solidification microstructure is critical to successful laser processing of single-crystal (SX) nickel-base superalloys and a practical tool for the microstructural control is processing–microstructure maps. However, the maps presented in literature do not consider the effects of powder feeding during laser additive manufacturing (LAM) of SX superalloys. This paper therefore presents a simple and feasible strategy to deal with the effects of powder feeding and to extend the combined numerical model used to calculate processing–microstructure maps. A characteristic ratio of epitaxial SX growth was defined to quantitatively compare the final solidification microstructure. Resulting processing–microstructure maps can estimate the influence of most processing variables, especially powder feeding rate, on the extent of epitaxial SX growth and the position of columnar-to-equiaxed transition. Using the processing parameters selected according to these processing–microstructure maps, a multi-layer SX deposit with fine dendrites was successfully fabricated by LAM. This successful SX LAM indicates that these new processing–microstructure maps involving powder feeding are reliable and useful because they can determine proper processing windows for LAM of SX superalloys and further advance the understanding of the processing–microstructure relationship in powder-feeding LAM process. [ABSTRACT FROM AUTHOR]

Gas tungsten arc welding was used to repair the laser additive manufactured Ti-5Al-5Mo-5V-1Cr-1Fe (Ti-55511) alloy with a subsequent triplex annealing treatment. The tensile properties of heat treated specimens containing of different proportions of weld zone were designed to evaluate the influence of weld zone on tensile properties of the alloy. Microstructures, microhardness and tensile tests were performed to study the mechanical properties and fracture behaviors of the specimens. Results show that dissolved oxygen in the weld zone has a strong influence on increasing the number of α phase nucleation sites that can lead to different α p morphologies in the base metal and weld zone. These different α p can lead to distinct microstructures after triplex annealing treatment but with similar α volume fractions. Besides, plasticity deterioration of the repaired tensile specimens is mainly attributed to the formation of columnar grain boundary α phases in the weld zone which are considered to be the earliest nucleation sites of microcracks and confirmed by in situ tensile test. With the increase of WZ proportions in the cross section of tensile specimens, the plasticity of the alloy gradually decreases. [ABSTRACT FROM AUTHOR]

A novel α+β titanium alloy with multi-alloying addition and low-cost is designed from Ti-6Al-4V. In order to maintain the same [Al] eq and [Mo] eq , the Mo and Zr were added into the alloy instead of V, and the nominal composition of this novel alloy is determined as Ti-6Al-2V-1.5Mo-0.5Zr-0.3Si with a spot of Si added. In this study, a plate of the novel alloy was manufactured by laser additive manufacturing (LAM). The macrostructure, microstructure, compositions, microhardness and room temperature tensile properties of as-deposited alloy were investigated. The results show that the macrostructure of the novel alloy contains large columnar grains and small columnar grains. Compared to the reference alloy Ti-6Al-4V manufactured with the same process, the novel alloy had much finer basket-weave microstructure. This novel alloy, solid-solute with alloying elements Mo, Zr and Si, has higher microhardness and better combination of strength and plasticity compared to Ti-6Al-4V. [ABSTRACT FROM AUTHOR]

Abstract: The compositional variation and the microstructural evolution in laser additive manufactured Ti/Ti–6Al–2Zr–1Mo–1V graded structural material were investigated. An anomalous compositional variation and its good correlation with hardness were found. Although, during the forming process, the ratio of Ti–6Al–2Zr–1Mo–1V in feeded powders abruptly changes from 0% to 100%, all the elements exhibit a gradual variation, which is preferred to a graded material because such gradient change can decrease the discontinuity of its microstructures and properties and can remarkably reduce the costs due to the simplified manufacturing process and the rational distribution of materials. [Copyright &y& Elsevier]