Characteristic effects of alloying elements on β solidifying titanium aluminides: A review.

Dynamic recrystallization and hot processing map of Ti-48Al-2Cr-2Nb alloy during the hot deformation

In this paper, Mg/Al laminated composites were successfully prepared at 400 °C by corrugated + flat rolling (CFR) with reduction ratios of 35% and 25% and subsequent annealing treatments were conducted at 200–350 °C for 30 min. A two-dimensional model was established to analyze the strain distribution during the first corrugated rolling process. Simulation results indicated that severe plastic deformation was formed at trough positions, which included more numerous refined grains than in the peak positions. The interfacial microstructure and mechanical property of the flattened composites along the rolling direction (RD) and the transverse direction (TD) were investigated. The results revealed that longitudinal discontinuous and transverse continuous interfacial intermetallic compounds (IMCs) were observed of the flattened as-rolled sample. Spatial distribution was provided for the grain microstructure along the thickness and rolling direction for AZ31B magnesium alloys of the CFR as-rolled composite. Mechanical property results showed that the longitudinal ultimate tensile strength (UTS) and elongation (EL) of the as-rolled sample reached 255 MPa and 4.14%, respectively. The as-rolled UTS along TD reached 325 MPa, about 30% higher than that along the RD. After heat treatment, the anisotropy of mechanical properties remained. The microstructure evolution and mechanical properties were discussed in detail.

Microstructure Characterization and Mechanical Property of Mg/Al Laminated Composite Prepared by the Novel Approach: Corrugated + Flat Rolling (CFR)

Theoretical investigation on the acoustic performance of Helmholtz resonator integrated microperforated panel absorber

Creep properties of ZK60 alloy and ZK60/SiCw composite have been investigated after extrusion and precipitation hardening by accelerated creep test. Creep tests were conducted at 150 °C in the stress range of 10–120 MPa. At low stresses, the stress exponents of 1.93 and 1.75 were obtained for the unreinforced alloy and the composite, respectively. Stress exponents of the unreinforced alloy and composite sample were 5.82 and 7.07, respectively, at high stresses. The creep mechanism changed by increasing the stress from grain boundary sliding (GBS) to dislocation creep due to the fact that the average true creep activation energy changed from 55 to 95.06 kJ/mol. Based on the microstructural observations, at low stresses, the grain refinement induced by twinning caused the GBS mechanism. However, at high stresses, slip changed from basal planes to the pyramidal secondary slip system which was associated with increase in twin density. Examination of the fracture surfaces revealed that cavity nucleation in the grain corners and around the precipitates was the main reason for creep failure.

Creep Behavior of ZK60 Alloy and ZK60/SiC w Composite After Extrusion and Precipitation Hardening

A particular structure that consists of four parallel-arranged perforated panel absorbers (PPAs) is proposed for the low frequency sound absorption within a constraint space. The apertures of the perforated panels are set to ≥1.5 mm, and the number of orifices is much less and therefore easier to be produced in comparison with that of the micro perforated panel (MPP). A simple approximation model by using acoustic-electrical analogy is described to calculate the sound absorption coefficient of such device subject to normal wave incidence. Theoretical and experimental results demonstrate that the device can provide more than one octave sound absorption bandwidth at low frequencies.

Design of Multiple Parallel-Arranged Perforated Panel Absorbers for Low Frequency Sound Absorption

A β-solidifying Ti-43Al-2Cr-2Mn-0.2Y alloy was directionally solidified by the optical floating zone melting method. The microstructure is mainly characterized by γ/α2 lamellae with specific orientations, which exhibits straight boundaries. The β phase is randomly distributed in the lamellar microstructure, indicating that the β phase cannot be directionally solidified. The directional solidification of γ/α2 lamellae was not affected by the precipitation of the β phase. Hot compression tests show that the deformation behavior of the β-containing lamellar microstructure also exhibits the anisotropic characteristic. The deformation resistance of the lamellae is lowest when the loading axis is aligned 45° to the lamellar interface. Microstructural observation shows that the decomposition of the lamellar microstructure tends to begin around the β phase, which benefits from the promotion of a soft β phase in the deformation. Moreover, the deformation mechanism of the lamellar microstructure was also studied. The bulging of the γ phase boundaries, the decomposition of α2 lamellae and the disappearance of γ/γ interfaces were considered as the main coarsening mechanisms of the lamellar microstructure.

https://www.mdpi.com/1996-1944/12/8/1203/pdf

The Directional Solidification, Microstructural Characterization and Deformation Behavior of β-Solidifying TiAl Alloy

A key challenge for direct methanol fuel cells is the sluggish reaction kinetics, poor anti-CO poisoning ability, and insufficient Pt utilization of platinum-based catalysts during methanol oxidation reaction (MOR). Herein, we report a facile approach for PtCuNi electrocatalysts with adjustable inner and surface configurations. By judiciously controlling the nucleation/growth kinetics, PtCuNi core-shell alloy nanoparticles (PtCuNi-CS NPs) fortified with a Cu-rich core and a Pt-rich shell are obtained. Especially, PtCuNi-CS NPs show the highest mass activity and specific activity toward MOR, 5.7 and 5.1 times higher than those of commercial Pt/C. Density functional theory calculations reveal that the PtCuNi-CS NPs with a suitable d-band center possess excellent electro-oxidation activity. Additionally, the doping of Cu and Ni atoms endows the PtCuNi-CS NPs with enhanced OH* adsorption. This work provides an effective design strategy to develop Pt-based trimetallic electrocatalysts as efficient anode materials for fuel cell applications.

Enhancing Electrocatalytic Methanol Oxidation on PtCuNi Core-Shell Alloy Structures in Acid Electrolytes.

In this paper, the microstructure, deformability, tensile properties, and phase hardness of the Ti–43Al–2Cr–0.7Mo–0.1Y alloy with a high β phase content were investigated. Microstructural analysis showed that the β phase precipitated not only at the colony boundaries but also inside the lamellae due to its high content. A high-quality forging stock was prepared through one-step noncanned forging. The total deformation reached above 80%, suggesting that the alloy has good hot deformability compared to other TiAl alloys. The deformed microstructure was composed of fine and equiaxed grains due to dynamic recrystallization. The high β phase content was shown to contribute to the decomposition of the initial coarse lamellae. Tensile testing showed that the alloy has good room-temperature ductility, even if the β phase content reaches above 20%. This is inconsistent with a previous study that showed that a large amount of the hard β phase is detrimental to the room-temperature ductility of TiAl alloys. Nanoindentation testing showed that the hardness of the β phase in the current alloy is about 6.3 GPa, which is much lower than that in the Nb-containing TiAl alloys. Low hardness benefits the compatible deformation among various phases, which could be the main reason for the alloy’s good room-temperature ductility. Additionally, the influence of various β stabilizers on the hardness of the β phase was also studied. The β phase containing Nb had the highest hardness, whereas the β phase containing Cr had the lowest hardness.

https://www.mdpi.com/1996-1944/12/17/2757/pdf

The Microstructural Evolution, Tensile Properties, and Phase Hardness of a TiAl Alloy with a High Content of the β Phase

The effect of heat treatment on the microstructures and mechanical properties of a novel β-solidifying Ti–43Al–2Cr–2Mn–0.2Y alloy was investigated. A fully lamellar (FL) microstructure with a colony size of about 100 μm was obtained by heat treatment at 1320 °C/10 min/furnace cooling (FC). A duplex (DP) microstructure with globular γ grains and γ/α2 lamellae was obtained by heat treatment at 1250 °C/4 h/FC. The residual hard–brittle β0 phase was also eliminated after heat treatment. The mechanical properties of the β-solidifying TiAl alloy depended closely on the heat treatment. The FL alloy had better fracture toughness, and the fracture toughness (KIC) value was 24.15 MPa·m1/2. The DP alloy exhibited better ductility, and the room temperature (RT) elongation of the alloy could reach 1%. The elongation of the alloy with different microstructures sharply increased when the temperature increased from 700 to 750 °C, indicating that the microstructure had no effect on the ductile–brittle transition temperature of the β-solidifying TiAl alloy. The fracture morphologies of different tensile specimens were observed. Interlamellar and translamellar fractures were the main fracture features of the FL alloy. Intergranular, translamellar, and interlamellar fractures were the main fracture features of the DP alloy.

Qianqian Wu

Papers

Design of Multiple Parallel-Arranged Perforated Panel Absorbers for Low Frequency Sound Absorption

The Directional Solidification, Microstructural Characterization and Deformation Behavior of β-Solidifying TiAl Alloy

Enhancing Electrocatalytic Methanol Oxidation on PtCuNi Core-Shell Alloy Structures in Acid Electrolytes.

The Microstructural Evolution, Tensile Properties, and Phase Hardness of a TiAl Alloy with a High Content of the β Phase

Effect of Heat Treatment on Microstructures and Mechanical Properties of a Novel β-Solidifying TiAl Alloy.