Structure and mechanical properties of extruded Mg–Gd based alloy sheet

The Mg–8Gd–2Y–1Nd–0.3Zn–0.6Zr (wt.%) alloy sheet was prepared by hot extrusion technique, and the structure and mechanical properties of the extruded alloy were investigated. The results show that the alloy in different states is mainly composed of α-Mg solid solution and secondary phases of Mg₅RE and Mg₂₄RE₅ (RE = Gd, Y and Nd). At aging temperatures from 200 °C to 300 °C the alloy exhibits obvious age-hardening response. Great improvement of mechanical properties is observed in the peak-aged state alloy (aged at 200 °C for 60 h), the ultimate tensile strength (σ_b), tensile yield strength (σ_0.2) and elongation () are 376 MPa, 270 MPa and 14.2% at room temperature (RT), and 206 MPa, 153 MPa and 25.4% at 300 °C, respectively, the alloy exhibits high thermal stability.     

Barrier capability of Zr–N films with titanium addition against copper diffusion

Zr–Ti–N film prepared by sputtering deposition has been employed as a potential diffusion barrier for Cu metallization. It is thought that the existing states of Ti and Zr in the films are Ti–N and Zr–N phase in Zr–Ti–N films. Material analysis by XRD, XPS and sheet resistance measurement reveal that the failure of Zr–N film is mainly due to the formation of Cu₃Si precipitates at the Zr–N/Si interface by Cu diffusion through the grain boundaries or local defects of the Zr–N barrier layer into Si substrate. In conjunction with sheet resistance measurement, XRD and XPS analyses, the Cu/Zr–Ti–N/Si contact system has high thermal stability at least up to 700 °C. The incorporation of Ti atoms into Zr–N barrier layer was shown to be beneficial in improving the thermal stability of the Cu/barrier/Si contact system.     

Assessment of the thermal stability of anodic alumina membranes at high temperatures

The thermal stability of anodic alumina membranes (AAMs) annealed in air from 750 °C up to 1100 °C was investigated. AAMs were produced by single-step anodising of laminated AA1050 in 0.30 M oxalic acid medium. The barrier layer provided thermal stability to the membranes, since it avoided or minimized bending and cracking phenomena. X-ray diffraction (XRD) analyses revealed that as-synthesized AAMs were amorphous and converted to polycrystalline after heat-treating above 750 °C. However, porous and barrier layers did not re-crystallize in the same way. The porous layer mainly crystallized in the γ-Al₂O₃ phase within the range of 900–1100 °C, while the barrier layer was converted to the α-Al₂O₃ phase at 1100 °C. Different grain sizes were also estimated from Scherrer's formula. Scanning electron microscopy (SEM) images pointed out that cell wall dilation of the porous layer explained membrane cracking, which was avoided in presence of the barrier layer.     

Wetting behavior of liquid Fe–C–Ti alloys on sapphire

Wetting behavior in the (Fe–C–Ti)/sapphire system was studied at 1823 K. The wetting angle between sapphire and Fe–C alloys is higher than 90° (93° and 105° for the alloys with 1.4 and 3.6 at.% C, respectively). The presence of Ti improves the wetting of the iron–carbon alloys, especially for the alloys with carbon content of 3.6 at.%. The addition of 5 at.% Ti to Fe–3.6 at.% C provides a contact angle of about 30°, while the same addition to Fe–1.4 at.% C decreases the wetting angle to 70° only. It was established that the wetting in the systems is controlled by the formation of a titanium oxicarbide layer at the interface, which composition and thickness depend on C and Ti contents in the melt. The experimental observations are well accounted for by a thermodynamic analysis of the Fe–Ti–Al–O–C system.     

Low-temperature compaction of Ti–6Al–4V powder using equal channel angular extrusion with back pressure

Equal channel angular extrusion (ECAE), with simultaneous application of back pressure, has been applied to the consolidation of 10 mm diameter billets of pre-alloyed, hydride–dehydride Ti–6Al–4V powder at temperatures ≤400 °C. The upper limit to processing temperature was chosen to minimise the potential for contamination with gaseous constituents potentially harmful to properties of consolidated product. It has been demonstrated that the application of ECAE with imposed hydrostatic pressure permits consolidation to in excess of 96% relative density at temperatures in the range 100–400 °C, and in excess of 98% at 400 °C with applied back pressure ≥175 MPa. ECAE compaction at 20 °C (back pressure = 262 MPa) produced billet with 95.6% relative density, but minimal green strength. At an extrusion temperature of 400 °C, the relative density increased to 98.3%, for similar processing conditions, and the green strength increased to a maximum 750 MPa. The relative density of compacts produced at 400 °C increased from 96.8 to 98.6% with increase in applied back pressure from 20 to 480 MPa, while Vickers hardness increased from 360 to 412 HV. The key to the effective low-temperature compaction achieved is the severe shear deformation experienced during ECAE, combined with the superimposed hydrostatic pressure.     

Microstructural investigations on as-cast and annealed Al–Sc and Al–Sc–Zr alloys

Al–Sc and Al–Sc–Zr alloys containing 0.05, 0.1 and 0.5 wt.% Sc and 0.15 wt.% Zr were investigated using optical microscopy, electron microscopy and X-ray diffraction. The phase composition of the alloys and the morphology of precipitates that developed during solidification in the sand casting process and subsequent thermal treatment of the samples were studied. XRD analysis shows that the weight percentage of the Al₃Sc/Al₃(Sc, Zr) precipitates was significantly below 1% in all alloys except for the virgin Al0.5Sc0.15Zr alloy. In this alloy the precipitates were observed as primary dendritic particles. In the binary Al–Sc alloys, ageing at 470 °C for 24 h produced precipitates associated with dislocation networks, whereas the precipitates in the annealed Al–Sc–Zr alloys were free of interfacial dislocations except at the lowest content of Sc. Development of large incoherent precipitates during precipitation heat treatment reduced hardness of all the alloys studied. Growth of the Al₃Sc/Al₃(Sc, Zr) precipitates after heat treatment was less at low Sc content and in the presence of Zr. Increase in hardness was observed after heat treatment at 300 °C in all alloys. There is a small difference in hardness between binary and ternary alloys slow cooled after sand casting.     

Creep deformation of Alloys 617 and 276 at 750–950 °C

Alloys 617 and 276 were subjected to time-dependent deformation at elevated temperatures under sustained loading of different magnitudes. The results indicate that Alloy 617 did not exhibit strains exceeding 1 percent (%) in 1000 h at 750, 850 and 950 °C when loaded to 10% of its yield strength (YS) values at these temperatures. However, this alloy was not capable of sustaining higher stresses (0.25YS and 0.35YS) for 1000 h at 850 and 950 °C without excessive deformation. Interestingly, Alloy 617 showed insignificant steady-state creep rate at 750 °C irrespective of the applied stress levels. Alloy 276 almost met the maximum creep deformation criterion when tested at 51 MPa–750 °C. Severe creep deformation of both alloys at 950 °C could be attributed to the dissolution of carbides and intermetallic phases remaining after solution annealing or precipitated during quenching.     

Effect of the long periodic stacking structure and W-phase on the microstructures and mechanical properties of the Mg–8Gd–xZn–0.4Zr alloys

Microstructures and mechanical properties of the Mg–8Gd–xZn–0.4Zr (x = 0, 1 and 3 wt.%) alloys, in the as-cast condition and the as-extruded condition, have been investigated. The results show that both the 14H long periodic stacking structure and the W-phase coexist together in the cast Zn-containing alloys. The volume fraction of the W-phase increases with increasing the addition of Zn. This phase is the crack source of the fracture. The 6H long periodic stacking structure is observed in the extruded Zn-containing alloys. The Mg–8Gd–1Zn–0.4Zr alloy exhibits the highest elongation, and the value of its elongation is 130% at 300 °C due to the refined microstructure. The W-phase plays an important role in improving the mechanical properties via pinning the movement of the grains at elevated temperature.     

Microstructure and mechanical property of laser melting deposition (LMD) Ti/TiAl structural gradient material

This article presents fabrication, microstructure and mechanical properties study of Ti/TiAl functional gradient material. Ti–47Al–2.5V–Cr/Ti–6Al–2Zr–Mo–V gradient material was successfully fabricated by the laser melting deposition (LMD) manufacturing process. Microstructure and chemical composition was characterized by OM, SEM, TEM and EPMA. The Vickers hardness and room-temperature tensile property was evaluated on longitudinal direction. Results showed that fully lamellar (FL) microstructure consisted of γ-TiAl and α₂-Ti₃Al was formed on the Ti–47Al–2.5V–Cr side, while coarse basket weave microstructure was formed on the Ti–6Al–2Zr–1Mo–1V side. No cracking was found in the gradient zone after aging at 800 °C for 48 h. The room-temperature tensile strength of the as-deposited specimen is up to approximately 1198.8 MPa in the longitudinal direction, while the tensile elongation is approximately 0.4%, indicating a typical brittle fracture.     

Bending strength and effective modulus of atmospheric ice

Bending strength and the effective modulus of atmospheric ice accumulated in a closed loop wind tunnel at temperatures − 6 °C, − 10 °C and − 20 °C with a liquid water content of 2.5 g/m³ have been studied at different strain rates. More than 120 tests have been conducted. Ice samples, accumulated at each temperature, have been tested at the accumulation temperature. In addition, tests have been performed at temperatures of − 3 °C and − 20 °C, for the ice accumulated at − 10 °C. These tests showed a clear dependency of bending strength of atmospheric ice on test temperature at low strain rates. Strain rate effects are implied because the spread in bending strength for the different temperatures diminishes as strain rate increases. The results also reveal that, in most cases, the effective modulus of atmospheric ice increases with increasing strain rate. The bending strength of atmospheric ice accumulated at − 10 °C has been found to be greater than that of ice accumulated at − 6 °C and − 20 °C. The results show that the effective modulus of ice accumulated at − 20 °C at higher strain rates is less than that of the two other types.     

A novel thermal treatment on a Mg–4.2Y–2.3Nd–0.6Zr (WE43) alloy

A double-stage thermal treatment has been adopted on a Mg–Y–Nd–Zr (WE43) alloy, following suggestions of a previous calorimetric investigation. A secondary precipitation is claimed to occur at a temperature as low as 150 °C after a preliminary precipitation at 210 °C, with the effect of enhancing the hardness increase and reducing the annealing times.     

Preparation and rheological behavior of lead free silver conducting paste

The lead free silver conducting pastes were prepared by using silver powder, lead free low-melting glass and terpineol ethyl cellulose solution. By analyzing the sheet resistance, Vickers hardness as well as the adhesion strength of the fired film by the pastes formulated with different content of the glass, the desired glass weight percentage was determined as 4–6 wt%. The films, prepared by the pastes using the lead free glass with a glass transition temperature of 488 °C, were perfectly flat and compact after fired at a peak temperature within the range from 540 °C to 590 °C. The sheet resistance of the fired film with glass content of 5 wt% was 2.3 × 10⁻³ Ω mm⁻² at the thickness of 15 ± 3 μm, while the Vickers hardness was 61 MPa, and the adhesion strength was 28.5 MPa. In addition, the rheological, thixotropic, and viscoelasticity behaviors of the typical paste characterized by using an ARES (RFS-III) rheometer, were similar to that of the screen printing paste with high solid filler. The pastes are applicable for manufacturing electrical components on glass substrate.     

Microstructure and mechanical properties of an HfB2 + 30 vol.% SiC composite consolidated by spark plasma sintering

An ultra-high-temperature HfB₂–SiC composite was successfully consolidated by spark plasma sintering. The powder mixture of HfB₂ + 30 vol.% β-SiC was brought to full density without any deliberate addition of sintering aids, and applying the following conditions: 2100 °C peak temperature, 100 °C min⁻¹ heating rate, 2 min dwell time, and 30 MPa applied pressure. The microstructure consisted of regular diboride grains (2 μm mean size) and SiC particulates evenly distributed intergranularly. The only secondary phase was monoclinic HfO₂. The incorporated SiC particulates played a key role in enhancing the sinterability of HfB₂. Flexural strength at 25 °C and 1500 °C in ambient air was 590 ± 50 and 600 ± 15 MPa, respectively. Fracture toughness at room temperature (RT) (3.9 ± 0.3 MPa √m) did not decrease at 1500 °C (4.0 ± 0.1 MPa √m). Grain boundaries depleted of secondary phases were fundamental for the retention of strength and fracture toughness at high temperature. The thermal shock resistance, evaluated through the water-quenching method, was 500 °C.     

Nanoscale dynamic wetting and spreading of molten Ti alloy on 6H–SiC

We have investigated nanoscale features at the reactive wetting front of the molten Ag–27.4 wt.% Cu–4.9 wt.% Ti on 6H–SiC using video movies recorded in situ on a high-temperature stage of a high-resolution transmission electron microscope and also proposed a model of a chemical reaction at each tip. One of the features of reactive wetting and spreading at 1073 K in 4 × 10⁻⁵ Pa was the discontinuous motion of the tip, and the halting time depended on the thickness of an amorphous Si–O layer on SiC, which can be explained by the time needed for the decomposition of the layer by Ti atoms to form TiC nanoparticles since Ti atoms in the molten alloy sufficiently rapidly diffuse to the tip on the SiC surface. Molten Ti and TiC nanolayers preceded the Ti₅Si₃ nanolayer at the tip. The reaction required to form the TiC nanolayer is also the rate-determining step for spreading. The contact angle of the tip increased up to 60–80° when the tip halted, whereas the tip decreased down to 10° on the nonbasal plane and 20° on the basal plane of SiC when it traveled rapidly. The high traveling angle of the molten tip on the basal polar plane of SiC indicates a high interfacial energy between Ti and SiC(0 0 0 1).     

ZnO sputter coating on SnO2 nanowires: Effects of thin coating and subsequent thermal annealing

The structural and optical properties of SnO₂–ZnO core–shell nanowires were studied and the effects of thermal annealing were investigated. As-prepared SnO₂–ZnO core–shell nanowires exhibited a smooth and continuous shell layer along the nanowire, with a thickness in the range of 5–10 nm. While the thin ZnO shell layer disappeared after annealing at 800 °C, this did not occur after annealing at 600 °C. The as-fabricated SnO₂–ZnO core–shell nanowires exhibited yellow emission, presumably from the core SnO₂ nanowires. The UV emission from ZnO shell layer was obtained by annealing at 600 °C, whereas it was removed by annealing at 800 °C.     

Prediction of crack depth during quenching test for an ultra high temperature ceramic

Quenching test was used to characterize thermal shock properties of ZrB₂–20%SiC_p–10%AlN. It showed that critical temperature difference was 400 °C, and residual strength was a constant while quenching temperature was higher than 400 °C. Inertial stress was investigated under different temperatures, as shown, a higher temperature led to a lower inertial stress. Crack resistance under room temperature was compared with that under 600 °C, as can be seen, a higher temperature led to a higher crack resistance. Dynamic thermal stress intensity factor was investigated at the quenching temperature of 600 °C, and it indicated that stress intensity factor ascended first and descended afterwards, farther crack propagation would not occur when Biot value is in a certain range, such as Biot = 5. Crack would not propagate when Biot = 1, and specimen would be destroyed when Biot = 10.     

Effect of Zr addition on the microstructure and properties of Cu–10Cr in situ composites

The Cu–10Cr–0.4Zr alloy and the in situ composites based on the alloy were prepared. Microstructure evolution and mechanical properties of Cu–10Cr–0.4Zr in situ composites were investigated. The results showed that the addition of 0.4 wt.% Zr in the Cu–10 wt.% Cr in situ composites gave birth to smaller as-cast Cr dendrites, which led to finer filaments at higher strain ratios. The ultimate strength of Cu–10Cr–0.4Zr composites reached 1089 MPa at draw ratio of η = 6.2, however that of Cu–10Cr prepared by the same procedure was only 887 MPa. The increasing strength of Cu–10Cr–0.4Zr in situ composites could be attributed to the combination of Hall–Petch strengthening of closely spaced Cr filaments, the strengthening effect of Zr and the strengthened Cu matrix.     

Microstructure and mechanical properties of Mg–4.5Al–1.0Zn alloy sheets produced by twin roll casting and sequential warm rolling

Microstructure and mechanical properties of Mg–4.5Al–1.0Zn (designated as AZ41M in short) alloy sheets produced by twin roll casting, sequential warm rolling and post annealing at 350 °C were studied in this paper. Microstructure of twin roll casting strip consisted of dendrite structure, eutectics and intermetallic compounds located in the interdendritic region. AZ41M alloy sheets showed higher strength and lower elongation after sequential warm rolling, while post annealing after warm rolling induced the decrease of strength and increase of elongation. This results in the balance of strength and elongation in AZ41M alloy sheets. The grain refinement during manufacturing processes was attributed to the formation of heavy shear bands, high dislocation density, twinning, and precipitates of Al₂Ca/Mg₂Ca or Al₈Mn₅ and the Ca dissolution into Mg₁₇Al₁₂ phase.     

Tribological behavior of NiTi alloy in martensitic and austenitic states

The wear behavior of Ti–50.3 at% Ni alloy in martensitic and austenitic states was studied. The alloy was prepared in a Vacuum Induction Melting furnace, forged at 800 °C, annealed at 1000 °C for 12 h, quenched in water, then aged at 400 °C for 1 h and followed by water quenching. The phase transformation temperatures were measured by differential scanning calorimetry. The shape memory and pseudoelasticity properties of NiTi were obtained by three-point bending test. The highest deflection recovery due to the pseudoelasticity was observed at temperature of 50 °C. The wear tests were conducted using a pin-on-disk tribometer in a water media at temperatures ranging from 0 °C to 50 °C. The results showed that the wear rate of NiTi alloy was decreased as the wear testing temperature increased. This was mainly attributed to the pseudoelasticity effect and higher strength of the alloy in the austenitic state at temperature of 50 °C. The results also showed a lower coefficient of friction in the austenitic state compared to the martensitic state.     

Serrated flow behavior in a near alpha titanium alloy IMI 834

Serrated behavior of near alpha titanium alloy IMI 834 has been studied at elevated temperature from 400 °C to 475 °C. Serrations morphology was found as A type of locking serrations followed by B type serrations at 400 °C. E type of serrations has been observed at higher strains at 425 °C. B type and unlocking serrations of C_A type at 450 °C and again A and C_B type serrations were found at 475 °C. In strength parameters, anomalous tensile behavior was found in the variation of tensile strength and yield strength with test temperature in the temperature range between 400 °C and 475 °C. However, the variation of normalized flow stress showed regions I–III with test temperature. Regions I and III correspond to normal tensile behavior and region II corresponds to anomalous tensile behavior. Blue brittle temperature of IMI 834 was attributed at 450 °C by confirming minimum ductility of 8.2%. In present study, a different approach has been adopted to show the change in deformation behavior during serrated region called as abrupt change in strain path. Maximum irregularity in flow behavior has been observed at 450 °C and 475 °C. Room temperature fractographic features showed transgranular features whereas mixed ductile and cleavage fracture has been observed in the temperature range between 400 °C and 475 °C. However, reverse slope behavior has been observed in the plot of critical strain versus test temperature at 450 °C, which could be due to silicide precipitation. In the present study, interaction of dislocations with interstitial/substitutional solutes is responsible for dynamic strain aging in IMI 834.