Wind turbine gears are critical components within the internal gearbox of the wind turbines. However, the vulnerability of gears to wear adversely affects their operational lifespan. Here, we propose ...a novel approach utilizing ultrasonic shot peening to incorporate Al2O3 particles onto the surface of the 18CrNiMo7–6, termed the USG treatment. The tribological test shows that the coefficient of friction and wear rate of the USG-treated sample decreased by 14.4% and 58.3% respectively, as compared to the untreated sample. Experiments and detailed analysis reveal that 18CrNiMo7–6 not only undergoes grain refinement on its surface but also forms a wear-resistant layer enriched with Al2O3. The findings here provide a new insight into the design of wear-resistant layers on gear steel surfaces.
Metastable β titanium alloys possess excellent strain-hardening capability, but suffer from a low yield strength. As a result, numerous attempts have been made to strengthen this important structural ...material in the last decade. Here, we explore the contributions of grain refinement and interstitial additions in raising the yield strength of a Ti-12Mo (wt.%) metastable β titanium alloy. Surprisingly, rather than strengthening the material, grain refinement actually lowers the ultimate tensile strength in this alloy. This unexpected and anomalous behavior is attributed to a significant enhancement in strain-induced α’’ martensite phase transformation, where in-situ synchrotron X-ray diffraction analysis reveals that this phase is much softer than the parent β phase. Instead, a combination of both oxygen addition and grain refinement is found to realize an unprecedented strength-ductility synergy in a Ti-12Mo-0.3O (wt.%) alloy. The advantageous effect of oxygen solutes in this ternary alloy is twofold. Firstly, solute oxygen largely suppresses strain-induced transformation to the α’’ martensite phase, even in a fine-grained microstructure, thus avoiding the softening effect of excessive amounts of α’’ martensite. Secondly, oxygen solutes readily segregate to twin boundaries, as revealed by atom probe tomography. This restricts the growth of {332} deformation twins, thereby promoting more extensive twin nucleation, leading to enhanced microstructural refinement. The insights from our work provide a cost-effective rationale for the design of strong yet tough metastable β titanium alloys, with significant implications for more widespread use of this high strength-to-weight structural material.
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Display omitted
Preventing columnar grain formation during additive manufacturing has become a significant challenge. Columnar grains are generally regarded as unfavourable as their presence can impart ...solidification defects and mechanical property anisotropy, however, the thermal conditions experienced during additive manufacturing make columnar grains difficult to avoid. In this work the thermal conditions during solidification (cooling rate, temperature gradients) are characterised during wire based additive manufacturing. For the selection of deposition conditions that favour equiaxed grain formation, the role of alloy constitution is explored in three classical alloy design regimes: an alloy containing no grain refiners (Ti6Al4V); an alloy only containing grain refining solutes (Ti3Al8V6Cr4Mo4Zr); and an alloy containing both grain refining solute and nucleant particles (Ti3Al8V6Cr4Mo4Zr + La2O3). Substantial refinement and equiaxed grain formation is achieved in the latter case which is attributed to β-Ti nucleation on La2O3. However, the thermal environment is dynamic during additive manufacturing and equiaxed grain formation is only achievable when temperature gradients decrease sufficiently to permit constitutional supercooling.
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Being lightweight, energy-efficient and environmentally benign, magnesium alloys present great potential for various industrial applications. However, they possess relatively low mechanical ...properties and need to be strengthened. During the last decade, significant effort has been directed towards preparation of strong nanocrystalline (NC) Mg alloys, although because of the limited plasticity inherent to HCP metals, the grain size of Mg was rarely refined below 1000 nm and the yield strength seldom exceeded 500 MPa. Here, by means of a conventional industrial method of rotary swaging, we prepared bulk NC Mg–Gd–Y–Zr alloys with an average grain size of 80 nm and a dimension of ∅3 mm × 1000 mm. The further-aged NC Mg alloy exhibits the yield strength of 650 MPa and the ultimate tensile strength of 710 MPa, the highest such values published for bulk Mg alloys. Fracture surface observation suggested a ductile inter-granular fracture in the NC Mg alloys. The high strength are attributed to nano-grain, intra-granular Gd rich clustering, inter-granular solutes segregation, β′ precipitation, dislocation and solution strengthening contributions, among which the nano-grain strengthening is dominant. The nano-grain formation results from the large number of mechanical twins, deformation bands and stacking faults induced by the high strain rate of swaging. Our work advances the industrial-scale production of bulk NC Mg alloys by exploring a simple and low-cost fabrication technique.
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•Rare earth (RE) containing Mg–Gd–Y–Zr alloy was successfully multidirectional forged for 8 passes without any cracks.•Initial coarse grains was refined due to a combination of discontinuous and ...continuous dynamic recrystallization.•The alloy MDFed after 6 passes exhibited an excellent balance of strength and ductility at room temperature.
A homogenized Mg–10Gd–4.8Y–0.6Zr (wt.%) alloy was subjected to multidirectional forging (MDF) at 773K. It was shown that the average grain size decreased with increasing cumulative strain till 6 passes. Uniform fine-grained structure with an average grain size of 9.3μm was achieved after 6 passes, i.e., cumulative strain of 1.8. Results revealed that grain refinement was induced by a complicated combination of discontinuous dynamic recrystallization at low strain regions and continuous dynamic recrystallization or rotation recrystallization at medium-to-high strain regions. The alloy multi-directionally forged (MDFed) for 6 passes exhibited an excellent balance of strength and ductility at room temperature with ultimate tensile strength (UTS) of 336MPa and elongation to fracture of 21.0%.
Recently, ferroelectric ceramics with high maximum polarization, low remnant polarization and high electric breakdown strength (BDS) have attracted much attention due to their potential applications ...in energy storage capacitors. In this work, we show a novel kind of (Ba,Sr)TiO3 (BST)-based lead-free ferroelectric ceramics, i.e., (1-x)Ba0.9Sr0.1TiO3-xBi(Zn0.5Zr0.5)O3 (BST-xBZZ) solid solutions, which were fabricated by the traditional solid-state reaction process. By introducing the BZZ into BST with a content from 0.05 to 0.20, purely pseudocubic perovskite phases and highly dense structures are obtained. The increase of the BZZ content not only shifts the TC toward to lower temperature, but also induces strong relaxor behaviors with diffuse phase transition characteristics, thus improving the temperature stability of dielectric properties. Of special interest is the improved energy storage properties, which were systematically evaluated by measuring the polarization-electric field (P-E) hysteresis loops as a function of electric field, frequency and loading cycle. It is found that BT-0.15BZZ ceramic achieves a maximum energy density of 1.11 J/cm3, which is attributed to the improvement of BDS. In addition, relatively good frequency stability and fatigue resistance of this composition suggest its potential application in energy storage devices.
Additive manufacturing (AM) is a new and promising production methodology adept at producing complex geometries, which can be optimized for lower weight and enhanced capabilities. The material ...properties of these additive components are dictated by the microstructures developed during processing, with a high sensitivity to grain structure and associated anisotropy. With this new processing modality comes the added difficulty of understanding the thermodynamics and kinetic mechanisms that dictate the evolution of microstructure. This research addresses the unique thermal conditions present in AM and the pathways for grain refinement in nanofunctionalized aluminum alloys. The Al-Ta system, in which Al3Ta intermetallic compounds are demonstrated to have substantial grain refining capacity, are the focus of this study. The grain size is shown to be reduced relative to pure aluminum by 1000X when tantalum is added at 1 vol%. The effectiveness of the Al3Ta intermetallic is dictated by the crystallography and availability of the inoculant phase under AM conditions.
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A novel Cu-2.5Fe-0.2Si-0.3Mg-0.3Cr-0.1Zr-0.2Y (wt.%) alloy is designed, which exhibits nice comprehensive properties under multi-stage thermo-mechanical processing, with a conductivity of 57.11 %IACS ...and a tensile strength of 672 MPa. The main secondary phases in the alloy include micron-scale FeCrSi and CuZrY phases, as well as nanoscale precipitate of FeCrSi. Conductivity and strength of the alloy are mainly improved by the precipitation of nanoscale FeCrSi phases, which increases dislocation obstruction and matrix purity. The (220) plane of the precipitate exhibits a 9.5° misfit angle with the (020) plane of the matrix under the 112 FeCrSi zone axis. The formation of low angle grain boundaries (LAGBs) results in significant grain refinement effects. The average grain diameter of the alloy is about 1.58 μm, which is related to the piles-up of dislocations along the boundaries and the different deformability between the micron-scale second phase and the matrix.
•Aging process is an effective strategy for precipitation strengthening and conductivity improvement in Cu–Fe alloy. However, the recrystallization effect eliminates work hardening, texture defects, and stress localization, making it difficult to combine precipitation strengthening with work hardening. Based on this, a novel Cu-2.5Fe-0.2Si-0.3Mg-0.3Cr-0.1Zr-0.2Y alloy is designed.•A low interface energy can be determined by the trace elements, so that recrystallization is hindered and refined crystal is observed.•The primary second phases also have a contribution to the grain refinement as a result of different deformability between the second phases and matrix.•Incoherent but tiny precipitates play a role on dislocation bypass strengthening and improving matrix purity. Tensile strength and electrical conductivity of the final state is 672 MPa and 57.11%IACS.
