In this work, the effects of substituting 3 wt% Gd with 3 wt% Y on the microstructure, mechanical properties, and corrosion behaviors in the Mg-Gd-Ni alloys were investigated. By substituting Gd with Y, the area fraction of bulk-shaped long-period stacking ordered phases (LPSO) increases, while one of eutectic Mg2Ni phase decreases slightly. Moreover, it also promotes the precipitations of lamellar LPSO phase and nanoscale stacking faults (SFs). The tensile tests showed that the addition of Y increased the yield strength by about 40 MPa, mainly due to the strengthening of the kink deformation of the bulk shaped LPSO phase, the hindering effect of the lamellar LPSO and SF on dislocation movement, and the strengthening caused by grain refinement. As a result, the Mg-5Gd-3Y–5Ni (MGYN) alloy exhibits excellent mechanical properties with tensile yield strength (TYS) of 288 MPa, ultimate tensile strength (UTS) of 364 MPa, and elongation (EL) of 8.3 %. Moreover, although the fraction of Mg2Ni phase with high electrochemical potential is decreased, the reduction in dissolution rate is not significant because the discontinuous distribution of lamellar LPSO in the grains intensifies the galvanic corrosion by increasing the proportion of cathode phase. As a result, the coexistence of Mg2Ni and LPSO phases can observably improve the dissolution rate. Finally, the highest dissolution rate (234.56 mg cm−2 h−1 in 3 wt% KCl solution at 93 °C) reported so far for the dissoluble magnesium alloys can be attained for MGYN alloy in this study. This work provides an economical material selection with high dissolution rate and sufficient strength for the fabrication of the fracturing plugging tools.

Mechanical training via cyclic loading and unloading was widely used in NiMnGa shape memory alloys (SMAs) to create single or double variant states for reducing the resistance to variant reorientation and thus achieving a maximum shape memory strain. In this work, an effort was made to reveal the deformation mechanism of a polycrystalline Ni52Mn27Ga17Co4 hightemperature SMAs consisting of non-modulated (NM) martensite with uniform orientation and surrounding gamma precipitates. The NM martensite microstructure was characterized as a selfaccommodated hierarchical twinned-structure prior to deformation. Based on the interrupted in-situ EBSD measurements and phase-field simulations, it was demonstrated that the compressive loading resulted in the thickening of the stress-favored variants with the <001>NM direction perpendicular to compression axis at different dimensional scales. The path consisted of two subsequent processes-first detwinning of the nano-lamellae within one micro-variant through inter-lamellae boundary motion, and then reorientation of micro-variants through inter-plate boundary motion. The Schmid factor and preferred orientation of nano-lamellae (or strain accommodation) dominated the entire detwinning/reorientation process of NM martensite. As a result, the hierarchically twinned microstructure almost evolved into a single-variant state with the disappearance of packet boundaries. The ductile gamma phase with network structure possessed more excellent strain-accommodated ability to the macroscopic deformation, hence significantly enhancing the mechanical properties including the ultimate compressive strength and elongation of NiMnGa SMAs.

Dissolvable magnesium alloys are receiving widespread attention recently, which are often designed by impurity elements alloying such as Ni and Cu. Herein, a ternary Mg-8Ni-4.2Cu (wt.%) alloy is firstly reported in which Ni and Cu are regarded as the main components. This alloy possesses a super-high corrosion rate of 303.1 mg center dot cm- 2 center dot h- 1 at 93 degrees C in 3 wt% KCl solutions, which was resulted from high potential difference between the secondary phases and Mg matrix, and the uniform distribution of secondary phases. This alloy also attains the decent mechanical properties, i.e., ultimate tensile strength (UTS) of 331 MPa and ultimate compressive strength (UCS) of 502 MPa, which are mainly from secondary phases strengthening, grain refinement, and dislocation strengthening. This work provides a qualified material selection for fabricating fracturing plugging tools.

Inferior absolute strength and dissolution properties are the main bottlenecks for the widespread application of dissolvable magnesium alloys in complex working environments for unconventional oil and gas resources. Here, a novel functional peak-aged Mg-9.5Gd-2.7Y-0.9Zn-0.8Cu-0.4Ni (wt.%) alloy for fracturing tools is reported, and it possesses an ultimate tensile strength of 457.6 MPa, ultimate compressive strength of 620.7 MPa and dissolution rate of ∼43.7 mg·cm−2·h−1 in 3 wt.% KCl solutions at 93 °C. The excellent strength of the aged-alloy is primarily attributed to the combination of grain refinement, long-period stacking ordered (LPSO) strengthening, and precipitation strengthening induced by stacking fault and β’ phase, among which the precipitation strengthening is dominant. Further investigations confirm that the corrosion is triggered from the micro-galvanic coupling between the Mg matrix and the cathodic lamellar and block LPSO phases. Strip-shaped corrosion pits along with LPSO phases are subsequently formed, significantly accelerating corrosion. The β’ precipitates can effectively improve the strength without compromising the dissolution rate because of their nanoscale size. This study provides an excellent material selection for dissolvable fracturing tools and presents a strategy by which a synergistic combination of strength and dissolution rate is achieved via peak-aging treatment.

Knowledge of transformation crystallography and variant organization of product phase was a prerequisite for tuning microstructure and enhancing functionalities in materials with displacive structure-transformation. However, the transformation orientation relationship (OR) between parent austenite and non-modulated (NM) martensite in traditional NiMnGa ferromagnetic shape memory alloy was not yet well-determined via direct experimental results, thus leading to ambiguity in understanding the self-accommodated configuration. In this work, by generating a microstructure with coexisting austenite and NM martensite through minor Co substitution and proper heat treatment, the transformation OR was unambiguously determined to be the N-W relation with {111}A//{101}NM and <2¯11>A//<101¯>NM on the basis of accurate EBSD orientation measurements. Analysis on deformation gradient matrix constructed from the N-W OR revealed that, the internal nano-twined structure allowed a maximum profit for eliminating the overall latticed deformation caused by transformation, overweighing the "sandwich" micro-variant pair structure. Such strain accommodation mechanisms consequently contributed to the resultant self-accommodated hierarchically twinned structure of martensite. Moreover, it was found that the prior austenite grain boundaries (PAGBs) provided dominated nucleation sites for NM martensite variants, where the preferential variant selection at PAGBs mainly depended on the inclination angle between the PAGB and matching close-packed direction (<2¯11>A//<101¯>NM) of variants. The present study provided comprehensive information on transformation crystallography and displacive characters of austenite to NM martensite transformation, which was useful for the efforts in property optimization and theoretical simulation.

Considerable interest to improve magnetic entropy change (ΔSm) and broaden working temperature interval (WTI) of NiMnGa ferromagnetic shape memory alloys (FESMAs) was stimulated by their applications as promising candidate materials for solid-state refrigeration. In the present study, we presented an approach to enhance the magnetocaloric properties of polycrystalline NiMnGa FESMAs via combining Dy micro-alloying and pseudoelastic cyclic training. The introduction of Dy elements established stable magneto-structural coupling transformation from the paramagnetic austenite to ferromagnetic martensite, accompanied by a large ΔSm [−16.42 J/(kg K)] and a widened WTI (∼15.98 K). Fascinatingly, it was demonstrated that the internal strain fields at phase interface between matrix and DyNi4Ga precipitates could assist the phase transformation nucleation, which significantly reduced the hysteresis loss from 20.84 J/kg of Ni54Mn25Ga21 alloy to 8.14 J/kg of Ni54Mn25Ga20.7Dy0.3 alloy. More importantly, the subsequent pseudoelastic cyclic training produced a strong ⟨110⟩NM preferred crystallographic orientation, which facilitated the magnetic alignment along easy magnetization axis. Consequently, the giant ΔSm value up to −24.25 J/(kg K) and effective refrigeration capacity RCeff of 198.77 J/kg were further achieved in the trained Ni54Mn25Ga20.7Dy0.3 alloy under an external magnetic-field change of 5.0 T.

Polycrystalline Ni54+xMn25Ga21-x high temperature shape memory alloys were developed to examine the Ni-content dependent crystallographic features, phase transformation and deformation behavior. The alloys were characterized by a hierarchically twinned martensite structure with the co-existence of ductile γ phase in Ni57 and Ni58 alloys. Two types of twinning relationships existed, i.e., (112) compound twin in the internal nano-lamellae and 11¯2 type-I twin in the adjacent micro-variants. The martensitic start temperature, compressive strength and ductility increased with increasing Ni content. However, the corresponding shape recovery capability was significantly deteriorated in the higher Ni-containing alloys. For the single-phase alloy, the detwinning/reorientation of internal nano-lamellae and activation of deformation twins contributed to the macroscopically recoverable strain in case of low pre-strains. In contrast, large pre-strains led to piles-up of dislocation, bending and kinking of twinning interfaces, formation of deformation bands and crossing of twin structures. These irreversible processes produced massive unrecoverable strain. Almost no detwinning and twining processes were observed in the dual-phase alloys due to the severe lattice distortion. Instead, most deformation occurred via dislocation motion in γ phase.

This study is to fabricate a composite substrate (Ni7W/Ni12W/Ni7W) with weak magnetization, strong reinforcement, and improved cube texture via Rolling Assisted Biaxially Textured Substrates (RABiTS) route. The formation of cube texture with reduction in twin boundaries due to recrystallization annealing was investigated thoroughly. The optimized recrystallization annealing process revealed 97.4% of cube texture and 83.9% of small angle grain boundaries at an angle of (<10°). Higher W content and presence of defects (holes, dislocations, and grain boundaries) within inner layer of the substrate restricted the formation of cube texture along the normal direction (ND), as compared to rolling direction (RD). Furthermore, significant improvement in mechanical strength (σ0.2 = 205 ± 2 MPa) and saturation magnetization (2.6 emu/g) was found for Ni7W/Ni12W/Ni7W as compared to Ni7.5W substrates.

Thin, reinforced and biaxially textured Ni5W/Ni12W/Ni5W composite substrate for coated conductor applications has been fabricated by traditional powder metallurgy method using the sparking plasma sintering (SPS) technology, followed by cold rolling and annealing. In-situ EBSD strain-stress analysis shows that the yield stress (δ0.2) can reach 240MPa. The high quality of cubic texture and boundaries of low misorientation angle were stable until elongations as high as 2%. Meanwhile, the cubic grain fractions on surfaces of top Ni5W layer of the composite tapes are 98.3%, 99.5% and 99.8%, respectively, corresponding to be annealed at 1250°C for 60min, 120min and 180min, indicating the cube texture can successfully sustain after severe treatment condition.

An in situ composite NixAly–Al2O3, with a near fully dense microstructure, is fabricated from Ni and Al elemental powders using the pre-oxidation and subsequent hot-press reactive synthesis (PORS) technique. The exact formula of the formed NixAly phase in the excessive Al-containing PORS1 and PORS2 samples deviates from the nominal stoichiometric one, dependent on the initial ratio of Ni to Al in the starting powder mixtures. Only NiAl compound is formed in the Ni50–Al50 (at.%) and Ni50–Al50 (at.%)–20 wt.% Al2O3 reaction systems during the hot-press reactive sintering process. The composites exhibit superiority to the NiAl monolithic compound in both flexural strength and fracture toughness at room temperature. Specifically, the in situ PORS1 composite has the highest room temperature flexural strength and fracture toughness with values of 453 MPa and 10.2 MPam, respectively. The toughening effect might be attributed to the interaction between the crack tip and components in the microstructure.

Porous ceramic with a framework structure of aluminum borate (9Al2O3·2B2O3) whiskers was in situ synthesized by firing above 1150°C a green powder compact of a mixture of aluminum hydroxide, boric acid and an additive of nickel oxide. During sintering, the whiskers of aluminum borate grew in situ in the compact, and were bonded together. The porous aluminum borate consisted solely of whiskers with a porosity of 54–58%. The average diameters of the whiskers increased from 0.2 to 2μm with increasing sintering temperature from 1150 to 1350°C. However, the estimated whiskers aspect ratio decreased with increasing sintering temperature.

Fe3Al-based composites reinforced with micron-sized titanium carbide, tetragonal zirconia and nano-scaled alumina particles were hot-pressed, and the room temperature mechanical properties were investigated. Results show that nano-Al2O3 is not an efficient ceramic for the enhancement of mechanical properties of Fe3Al, primarily due to its inhomogeneous distribution and severe agglomeration within the matrix as well as the weak interfacial bonding. By contrast, Fe3Al/5 wt.% ZrO2 composite had a strength as high as 1361 MPa and a fracture toughness of 19.0 MPa m. The enhancing effect is attributed to the low thermal expansion mismatch between ZrO2 and Fe3Al matrix, and to the stress-induced transformation of ZrO2 particles. The flexural strength and fracture toughness for Fe3Al/10 wt.% TiC composite was 1086 and 20.0 MPa m, respectively. The mechanical properties of Fe3Al/TiC composites decreased with TiC content above 10 wt.% due to the suppression of plastic deformation, residual porosity and interfacial debonding.

A new in situ multi-phase composite based on intermetallic TiAl is successfully reaction-synthesized from elemental powder mixtures of Ti, Al, TiO2 and C using hot-pressing-aided reaction synthesis technique (HPRS). The microstructure, flexural strength as well as fracture toughness of the monolithic TiAl-based compound and in situ composites are investigated. The products are mainly composed of Al2Ti4C2, TiC, Al2O3, Ti3Al and TiAl whereas Al3Ti is formed in case the starting powder mixtures contain more excess amount of Al. It is found that the formed fine Al2O3 and TiC particles tend to disperse on the grain boundaries. Although all of the three materials exhibit a typical brittle fracture mode, the fracture toughness of the in situ composites is substantially higher than that of the monolithic TiAl-based alloy by about 40–60% increase due to the toughening effect arising from interaction between the crack tip and the microstructures. However, the existence of residual porosity in the in situ composite samples in case of low external pressure applied to compacts during the reaction synthesis process results in insuperior flexural strength to that of the TiAl-based monolithic.

Ti–Al3Ti laminated composites have been fabricated through reactive sintering in vacuum using Ti and Al foils with different initial thickness. The aluminum layer was completely consumed resulting in microstructures of well-bonded metal–intermetallic layered composites with Ti residual metal layers alternating with the aluminide intermetallic layers. The MIL composites exhibit a very high degree of microstructural design and control. Microstructure characterization by scanning electron microscopy (SEM), X-ray diffractometry (XRD) and energy dispersive spectroscopy (EDX) has shown that Al3Ti is the only titanium aluminide phase due to the thermodynamics and phase selection of the reaction between Ti and Al through mass diffusion in the presence of liquid Al. The mechanical properties and fracture behavior of the fabricated laminated composites were examined through three-point bending test. The results indicated that the composites exhibited anisotropic features. When the load perpendicular to the laminates was applied, they displayed a step-like or saw-tooth load–displacement response and superior flexural strength as well as fracture toughness, which is also dependent on the number and thickness of individual layers. A non-catastropic fracture was observed in the laminated composites due to the deflection of cracks along the Ti/Al3Ti interface. The Ti layer failed by cleavage mode, showing extensive plastic deformation during the bending process.

Ti–Al3Ti laminated composites have been fabricated through reactive sintering in vacuum using Ti and Al foils with different initial thicknesses. The aluminum layer is consumed by forming a titanium aluminide intermetallic compound. Thus, the final microstructure consists of alternating layers of intermetallic compound and unreacted Ti metal. Microstructural characterization by scanning electron microscopy (SEM), X-ray diffractometry (XRD) and energy dispersive spectroscopy (EDX) has shown that only the intermetallic Al3Ti is formed, which can be rationalized in terms of thermodynamics and kinetics of phase selection, as well as by the diffusion processes occurring in the presence of liquid Al.

Mo–Si–Al–C-based multiphase compounds and their composites reinforced by micro-SiC and TiC particulates were manufactured by means of reactive hot-pressed sintering method. Their microstructure and room temperature mechanical properties were studied. The results showed that Al addition and the ratio of Si/Al exerted a remarkable effect on the reaction products in the Mo–Si–Al–C systems. For the stoichiometric Mo5(Si,Al)3C mixed powders with a molar ratio of Mo:Si:Al:C as 5:1.5:1.5:1, the sintered body contained Mo3Si, Mo3Al2C, and Mo5Si3C as the major reaction products whereas and the minor phases consisted of MoSi2, Mo2C, and Mo(Si,Al)2 compounds. When the starting powder mixture was off-stoichiometric with a small amount of excess Si, only Mo2C accounted for the minor product. Moreover, the relative contents of the former three major phases were affected by the changed Si/Al ratio, where the amounts of Mo3Al2C and Mo5Si3C compounds decreased and increased, respectively with increasing Si/Al ratio. The two multiphase alloys showed poor mechanical properties, due to the existence of residual porosity. In contrast, the composites exhibited superiority in both flexural strength and fracture toughness at room temperature to the Mo–Si–Al–C-based multiphase compounds. MSAC1/20wt.%SiC and MSAC1/20wt.%TiC composites had a respective flexural strength and fracture toughness of 454 and 438MPa, 4.93 and 4.85MPam.