Abstract: Bulky sample was made by using TIG wire and arc additive manufacturing (WAAM) technology, in which Ф1.6 mm filler wire of in-situ TiB2/Al-Si composites was selected as deposition metal, following by T6 heat treatment. The microstructure and mechanical properties of the bulky sample before and after heat treatment were analyzed. Experimental results showed that the texture of the original samples parallel to the weld direction and perpendicular to the weld direction was similar consisting of columnar dendrites and equiaxed crystals. After T6 heat treatment, the hardness of the sample was increased to 115.85 HV from 62.83 HV, the yield strength of the sample was 273.33 MPa, the average tensile strength was 347.33 MPa, and the average elongation after fracture was 7.96%. Although pore defects existed in the fracture, yet the fracture of the sample was ductile fracture.
Abstract: The properties of titanium alloys significantly depend on the microstructure, which are correspond to the deformation conditions. However, because of its low thermal conductivity, sensitive to deformation temperature, narrow stable regions for hot working and structural heterogeneity, it does not achieve cosmically industrial production and application. In this paper, the effects of hot rolling deformation in single-phase (β) region, cross-phase region and heat treatment on the microstructure and mechanical properties of Ti-6Al-4V ELI alloy were systematically investigated. The relationship between microstructure and properties of alloy was also analyzed in order to a theoretical basis for the development of the rolling technology for the manufacture. The results indicated that hot rolling deformation in different region had significant effects on microstructure heterogeneity (the size and colony of α phase, lamellar microstructure of β transformed). It has been shown that fine and coarse lamellar α structure within grains and visible grain boundary α were characterized after the deformation above the β transformation temperature, which made high impact toughness. But in order to ensure in single phase region, the heat preservation method after passes of rolling may cause β grain coarsening (widmanstatten structure), leading to mechanical properties worsen. The fine crisscross substructures of α phase was obtained after deformation in cross-phase region, improving good mechanical properties. After solution treatment followed aging, the uniform type of microstructure was reached, which mainly displayed the change of contents and sizes of lamellar α phase.
Abstract: At present, domestic cold-rolled titanium sheets have many surface defects, which are significantly different from foreign surface quality. This paper mainly studies the differences in the microstructure and performance of titanium plates GR1 and GR2 imported from Japan and domestic titanium plates TA1, and analyzes the causes of surface defects to solve the problem about TA1. The surface properties of different materials were observed. The mechanical properties of the materials were obtained by room temperature tensile test. The surface roughness of the three materials was tested. The microstructure and composition of the three materials were characterized by SEM, EDS and XRD. The results show that the surface of GR1 and GR2 is brighter and has no obvious chromatic aberration. The surface chromatic aberration of TA1 is larger. The mechanical properties of TA1 are the best. The tensile strength and yield strength of rolling are 325.19MPa and 271.17MPa, respectively, and the lateral direction is 329.19MPa and The roughness of 303.15MPa, GR1 and GR2 is slightly lower than that of TA1. The black area on the surface of TA1 is loose and the oxygen content is high. The pole figure of GR1, GR2 and TA1 are obtained. Keywords: Cold-rolled titanium sheets; Chromatic aberration; Mechanical properties; SEM; Texture
Abstract: With the development of lightweight vehicles, aluminum alloy sheets are increasingly used in the automotive field. However, the aluminum alloy sheet has poor forming performance at room temperature. Therefore, how to improve the sheet metal forming performance of aluminum alloy sheet has become one of the current research hotspots. In this paper, the effects of different lubricants on the deep drawing forming properties of 6061 aluminum alloy sheets were studied by cupping experiments. The effects of lubricants on the deep drawing of sheet metal forming and the wall thickness of cups after deep drawing were explored. The results show that under the condition of drawing speed of 3MPa and 200mm/min, the ultimate drawing ratio of the sheet under oil lubrication is 1.92, and the PTFE film is 2.16. Grease and graphite lubrication are respectively 2.12 and 2.03, using PTFE film lubrication can increase by about 10% contrast with the oil lubrication. The measurement of the wall thickness of the cup under the forming limit state shows that the position with the largest reduction rate appears in the rounded transition zone, and the wall portion of the cylindrical member increases with the height of the wall, and the thickness from the bottom of the cup to the bottom of the cup. The edges all show a trend of decreasing first and then increasing.
Abstract: The served harsh environment of advanced aircraft engine puts forward higher requirements for high temperature titanium alloy performance. The optimized heat treatment technology provides effective theoretical basis for improving the microstructure and properties of high temperature titanium alloys. In this paper, we study the influence of different heat treatment systems on microstructure and mechanical properties of high temperature alloy with equiaxed structure, in order to obtain the corresponding relationship between the process and the microstructure performance of the alloy and the optimal heat treatment process. Analysis the effect of solution treatment on the primary α phase quantitatively by optical microscope and Image-Pro-Plus 6.0 software based on the forged high temperature titanium alloy in α+β phase region. Observe the precipitation of α2 phase and silicide by TEM, optimize the aging process according to hardness test. The results show that the content of primary a phase decrease from 63.3% at 920°C to 15.3% at 990°C with the increase of solution temperature. When the temperature rises to 980~990°C, the structure changes from equiaxed structure to α+β duplex microstructure. And change into lamellar structure when the solution temperature raise to 1010°C. The secondary α phase precipitates more fully when the aging temperature increases. And with increasing aging time, the trend of α2 phase growth become more significantly. The optimum heat treatment system obtained in this experimental is 990°C/1h/AC+700°C/5h/AC, and the α phase is about 15.3%. Hence, the excellent microstructure and properties match has been obtained.
Abstract: In this paper, a typical new zirconium alloy (Zr-Sn-Nb system) was used as the research object. The zirconium alloy strip was prepared from a series of production processes from smelting. By optimizing the process of cold processing with the change of the deformation amount and the intermediate heat treatment, the mechanical properties of the zirconium alloy were studied by different processing. The results are as follows: (1) The mechanical properties of the new zirconium alloy have reached the mechanical properties of Zirlo alloy with the optimization of the alloy composition, and (2) The zirconium alloy can refine the grain strength by the control of deformation degree and annealing temperature during cold deformation. The larger of the cold deformation, the smaller the average of the grains and the higher the yield strength of the material. The yield strength of the material was decreased by cold rolling and annealing more than once; (3) The larger the cold rolling variable of the zirconium alloy in cold deformation, it is beneficial to the second phase to be fine, dispersed and uniformly distributed, thus improving the strength of the material.
Abstract: Ti-6.5Al-2Zr-1Mo-1V (TA15) and Ti-6.5Al-3Sn-3Zr-3Mo-3Nb-1W-0.2Si (BTi-6431S) dissimilar titanium alloy plates were welded through electron beam welding (EBW) method and different ultrasonic impact treatment (UIT) technologies were performed on the weldment. The effects of UIT on the microstructure and residual stress distribution and mechanical properties for the welding joint were investigated. A significant microstructural change occurs after welding. The structure of welding joint is composed of fusion zone (FZ), heat-affected zone (HAZ) and base metal. The microstructure of FZ is composed of martensite structure and a clear interface is observed because of the fusion of dissimilar alloys. HAZ near fusion zone is comprised of martensite structure, while the grain size is much smaller than that in FZ. The HAZ microstructure near TA15 alloy is composed of coarse equiaxed α phases and HAZ microstructure near BTi-6431S alloy is lamellar α phases. Through ultrasonic impact treatment for three times, the residual stress near the welding joint shows a uniform distribution and the maximum tensile stress changes to compressive stress. A characteristic asymmetrical microhardness profile is observed in TA15/BTi-6431S dissimilar alloy welded joint. The HAZ in BTi-6431S alloy side possesses higher hardness compared with that in TA15 alloy side. The microhardness and tensile properties change slightly after ultrasonic impact treatment.
Abstract: The oxidation behavior and mechanism of Ti-Cu alloys (0≤w(Cu)≤20%) in the temperature range of 1000°C～1300°C are studied by thermogravimetric analysis(TGA) combined with SEM, EDS and XRD analysis methods. The results show that the oxidation rates of Ti-Cu alloys increase sharply when the temperature rises above 1000°C. The oxidation products have a three-layer structure, from the outside to the inside, which are dense outer oxide layer of TiO2, porous inner oxide layer of low valence oxide of Ti and Cu-enriched layer. With the increase of the temperature, the thicknesses of oxide layers of Ti-Cu alloy increase and the Cu-enriched phase increases gradually and melts. The melting Cu-enriched phase flows to the oxidation surface along the grain boundaries of the oxide layer. The high temperature oxidation resistance of Ti-Cu alloys declines with the increase of Cu content. The main reason is that more liquid Cu-enriched phase is formed and flows to the oxidation surface along the oxide grain boundaries in the Ti-Cu alloy, and Ti and O ions can diffuse more easily along the liquid Cu-enriched phase, which increases the oxidation rates.
Abstract: This article investigated the fatigue crack growth behaviors in the novel TC32 titanium alloy with bimodal and basket-weave microstructures, which were respectively obtained by the convectional (α+β) phase forging and quasi-β forging processing. Results showed that at the same level of tensile performance, the basket-weave microstructure had a lower fatigue crack growth rate than the bimodal microstructure, as the basket-weave microstructure had a more tortuous crack path, a rougher fracture surface and more secondary cracks. All these served to improve the fatigue crack growth resistance, which attributed largely to the effects of crack closure. Moreover, secondary cracks grew primarily along the α/β interfaces for the basket-weave microstructure but directly went across the colony-type lamellar (α+β) phase and the primary α phase without obvious regularity for the bimodal microstructure.
Abstract: The effects of the contact pressure Pfric and the oxygen concentration c0 on the ignition resistance of Ti-6Al-4V were studied by friction in oxygen-enriched atmosphere. The relationship of Pfric-c0 was built to quantitatively describe the ignition resistance, the combustion microstructures were investigated by XRD, SEM and EDS. Further, the principle of improving the ignition resistance was proposed. It indicates that the relationship of Pfric-c0 obeys parabolic law. The c0 decreases by 4% when the Pfric increases from 0.1MPa to 0.25MPa, manifesting that the ignition resistance depends on c0 strongly (or equivalent flow pressure Peq). The ignition resistance of Ti-6Al-4V is 42.9% of that of TB12. When Peq varies from 0.1~0.5MPa, the critical ignition temperature Т* is approximate to 568~461K. Violent sparks form during frictional ignition. The low ignition resistance of Ti-6Al-4V probably results from not only the composite oxides of TiO2, Al2O3 and V2O5 generating during ignition which could not prevent the rapid interaction between Ti and O, but also the Al and V elements in the heat-affected zone which could not stop or slow the massive diffusion of O towards the alloy.