Journal of Materials Engineering and Performance

Partially aged 6061 aluminum plates were welded by the gas metal arc welding process. During the welding process, a cooling system to act as a heat sink was used to extract the heat coming out from the welding process. To determine the experimental weld thermal cycles, K type thermocouples were placed at the heat affected zone. Finite element was used to compute the thermal distribution and isothermal sections generated by welding. The temperature measurements, Vickers microhardness profiles and tensile tests were observed to be related with the microstructural β″ to β′ phase transformation. The over-aging of the heat affected zone tends to diminish when the heat sink is used as compared with the reference welding condition. An increase on tensile strength (about 5.8%) and ductility (close to 29%), for welds performed in partial aging materials with respect to the welds with artificial aging condition (6061-T6 alloy) was also observed.

By applying the TC4-Ti2AlC composite coatings to the Ti6Al4V substrate by laser, the wear resistance of the Ti6Al4V alloy was improved. Analysis was done on the composite coatings' microstructure, phase composition, microhardness, and tribological characteristics. According to the findings, coatings without defects can be created when Ti2AlC content ranges between 5 and 15 wt.%. Furthermore, the coating without Ti2AlC consisted of a α-Ti solid solution while coatings with Ti2AlC included a α-Ti solid solution, hard phases of TiC and Ti3Al, as well as a Ti2AlC ceramic phase. During laser cladding, Ti2AlC partially dissolved and turned into TiC and Ti3Al, resulting in an average hardness of 371.61 ± 3.95 HV0.5, 382.92 ± 3.61 HV0.5, 388.91 ± 3.29 HV0.5 for the coatings with Ti2AlC weight fractions of 5, 10, and 15%, respectively. These numbers were about 1.16 ~ 1.22 times the hardness of the titanium alloy matrix (320 ± 3.12 HV0.5). Besides, the Ti2AlC lubricant and hard phases act synergistically to bring composite coatings better performances in wear resistance and friction reduction compared to the pure TC4 coating. The lowest coefficient of friction (0.382) (COF) and the greatest wear resistance (8.87 × 10−5 mm3/N m) were obtained at the composition of TC4-10wt.%Ti2AlC; more particularly, the wear resistance at TC4-10wt.%Ti2AlC was 1.2–2.1 times that of pure TC4 coating. The principal causes of wear in a pure TC4 coating are adhesive wear and oxidation, however, these wear processes shift to minor abrasive wear and oxidation when assisted by oxide coatings, Ti2AlC lubricant, and TiC, Ti3Al hard phases.

In this paper, the hot-rolled annealed Zircaloy-4 samples with different orientation were subjected to uniaxial compression with a strain rate of 0.001 s−1 to obtain the stress-strain curves of different initial orientation samples at different temperatures. Electron backscatter diffraction (EBSD) technique and transmission electron microscope (TEM) technique were used to analyze the microstructures and textures of compressed samples. The mechanical properties and microstructural evolution of rolling directions (RD), transverse directions (TD) and normal directions (ND) were investigated under the conditions of – 150 °C low temperature, room temperature and 200 °C high temperature (simulated lunar temperature environment). The results show that the strength of Zircaloy-4 decreases with the increase in deformation temperature, and the strength in three orientations is ND > TD > RD. The deformation mechanism of hot-rolled annealed Zircaloy-4 with different orientation is different. In RD, $$\{ 10\bar{1}0\}$$ $$\left\langle {\text{a}} \right\rangle$$ prismatic slip has the highest Schmid factor (SF), so it is most easy to activate the slip, followed by TD orientation, and ND orientation is the most difficult to activate. The deformed grains abide slip→twinning→slip rule, and the different orientation Zircaloy-4 deformation mechanisms mainly are the twinning coordinated with the slip.

Recently, absorption of vibration energy by mechanical damping has attracted much attention in several fields such as vibration reduction in aircraft and automotive industries, nanoscale vibration isolations in high-precision electronics, building protection in civil engineering, etc. Typically, the most used high-damping materials are based on polymers due to their viscoelastic behavior. However, polymeric materials usually show a low elastic modulus and are not stable at relatively low temperatures (≈323 K). Therefore, alternative materials for damping applications are needed. In particular, shape memory alloys (SMAs), which intrinsically present high-damping capacity thanks to the dissipative hysteretic movement of interfaces under external stresses, are very good candidates for high-damping applications. A completely new approach was applied to produce high-damping composites with relatively high stiffness. Cu-Al-Ni shape memory alloy powders were embedded with metallic matrices of pure In, a In-10wt.%Sn alloy and In-Sn eutectic alloy. The production methodology is described. The composite microstructures and damping properties were characterized. A good particle distribution of the Cu-Al-Ni particles in the matrices was observed. The composites exhibit very high damping capacities in relatively wide temperature ranges. The methodology introduced provides versatility to control the temperature of maximum damping by adjusting the shape memory alloy composition.

A tantalum carbide (TaC) ceramic layer was produced on gray cast iron matrix by in situ technique comprising a casting process and a subsequent heat treatment at 1135 °C for 45 min. Indentation fracture toughness in TaC ceramic layer was determined by the Vickers indentation test for various loads. A Niihara approach was chosen to assess the fracture toughness of TaC ceramic layer under condition of the Palmqvist mode in the experiment. The results reveal that K IC evaluation of TaC ceramic layer by the Vickers indentation method strongly depends on the selection of crack system and K IC equations. The critical indentation load for Vickers crack initiation in TaC ceramic layer lies between 1 and 2 N and the cracks show typical intergranular fracture characteristics. Indentation fracture toughness calculated by the indentation method is independent of the indentation load on the specimen. The fracture toughness of TaC ceramic layer is 6.63 ± 0.34 MPa m1/2, and the toughening mechanism is mainly crack deflection.

H13 steel is a typical hot work die steel with good strength and toughness that is often used to manufacture high-temperature disk springs. However, disk springs occasionally fail after use in the petrochemical industry. Therefore, the effects of the quenching and tempering temperatures on the microstructure and mechanical properties of H13 steel after quenching and tempering processes are investigated herein. The results show that the lath width (lath) controls the strength of the H13 steel. The precipitated phases mainly comprise Cr23C6, Cr7C3 and VC. The coarsening of the Cr23C6 phase reduces the hardness, while reducing the dislocation density improves the toughness of the H13 steels after quenching and tempering. When the quenching temperature is 1040 °C and the tempering temperature is 570 °C, the H13 steel after quenching and tempering has a uniform microstructure with good strength and toughness.

The N-bearing 19Cr-LDSS (Lean Duplex Stainless Steel, LDSS) with heterostructure consisting of coarse-grained ferrite and ultrafine-grained austenite was prepared by combining severe plastic deformation with High Temperature-Short Time (HTST) heat treatment. The microstructural observations and measurements were performed on deformed and annealed samples to correlate the excellent strength-plasticity matching to the grain refining and transformation-induced plasticity (TRIP) effect. The heterogeneous structure revealed a remarkable improvement of the strength compared to the counterparts processed by the conventional solution treatment. A yield strength (YS) of 800 MPa, ultimate tensile strength (UTS) of 1100 MPa and total elongation (TE) of 45% were achieved by the HTST treatment. Therefore, the higher YS and UTS of 19Cr-LDSS under HTST treatment were obtained on the premise of ensuring the excellent strength-plasticity matching. The high strength was provided by the grain refinement, and the high uniform elongation was attributed to the persistent high strain hardening rate due to the hetero-deformation-induced stress associated with the activation of TRIP effect. Meanwhile, the strain accommodation of coarse-grained ferrite phase also contributed to the improvement of plasticity for the experimental steel.

Duplex structural stainless steels (DP) are highly corrosion-resistant with austenite (γ)-ferrite (δ) compositions and processing routes. These DP steels are used in chemical, petrochemical, marine, power generation, and nuclear industries due to their unique properties. Experimental data of 2D slices obtained from optical micrography were used in a multilevel finite element analysis to investigate the interface stresses between the two phases of DP material. Level #1 (macro-level) finite element analysis involves homogenizing the 2D slices based on their representative constituent properties to identify high-stress regions. Level #2 (micro-level) finite element analysis was conducted with representative austenite/ferrite microstructure identified from level #1 analysis. The results from finite element simulations from both macro- and micro-levels revealed that interface stresses are affected by the phase’s microstructure distributions. Micro-level analysis revealed maximum interface stress is much higher than macro-level analysis. It was also found that stress localization occurred at the ferrite/austenite interfaces based on their distributions.

For TA15 Ti alloy, which has been widely used to form key load-bearing components in aeronautic and space fields, particular performances and corresponding microstructures are demanded due to various service environments. By applying single-phase field heat treatment, single-phase + two-phase field heat treatments, forging (α + β phase zone) combined with high-temperature aging and dual heat treatment, four types of microstructures, namely the fully lamellar microstructure, basket weave microstructure, two-phase composite microstructure and tri-modal microstructure, were obtained, respectively. And after conducting mechanical property tests for these microstructures, it was found that enhancing the lamellar thickness in the fully lamellar microstructures, reducing the content of equiaxed α phase to about 20% or increasing the content of lamellar phase in the two-phase composite microstructures and controlling the content of equiaxed α phase within 20% in the tri-modal microstructure were beneficial for performance improving. In addition, two-phase and three-phase composite microstructures possessed excellent comprehensive mechanical properties, and fully lamellar microstructures had the highest fracture toughness.