Ti-free Alloy Research Articles

Enhancing mechanical properties and corrosion resistance of Fe–Cr–B–Mo alloy via the 'Divide and Conquer' strategy for Ti regulation

The corrosion of molten aluminium on components in the aluminium industry poses a significant bottleneck, hindering the development of aluminium products and equipment. This study focused on the Fe–Cr–B–Mo alloy, addressing challenges related to the susceptibility of the matrix to corrosion, the excessive brittleness of M2B borides (M = Fe, Cr, etc.), and the detachment of corrosion products. A comprehensive study was performed to study the microstructure evolution, mechanical properties, and corrosion behavior of Fe–Cr–B–Mo alloy, considering the 'Divide and Conquer' strategy for Ti regulation. The findings indicate that the heterogeneous nucleation, induced by in situ TiB2 particles, significantly impacts the refinement of M2B borides size and enhances the matrix strength. Notably, the addition of 4.5 wt. % Ti to the T3 alloy significantly enhances its mechanical properties and corrosion resistance. The T3 alloy exhibits an impact toughness of 32.4 kJ/m2 and a compressive fracture strain of 19.5 %, representing a considerable increase of 58 % and 167 % over the Ti-free alloy, respectively. Furthermore, the alloy has a volume loss rate of 11.0 mm3 cm−2 h−1, which is substantially lower, by 73.5 % compared to H13 steel and by 21.4 % compared to the Ti-free alloy. The synergistic presence of TiB2 and M2B borides, along with their corrosion products, functions as an effective diffusion barrier against molten aluminium corrosion.

Effect of Ti content on microstructure and properties of Al-9.9Zn-2.6Mg-0.91Cu-0.2Zr-xTi aluminum alloy

The effects of different Ti contents of 0, 0.34 wt% and 0.81 wt% on the microstructure and properties of hot extruded Al-9.9Zn-2.6Mg-0.91Cu-0.2Zr-xTi alloy were studied by means of metallographic analysis, XRD analysis, hardness and conductivity test, tensile property test and corrosion test. The results show that the addition of Ti in the alloy can inhibit recrystallization and grain growth, and can refine the grain obviously when the solid solution treatment is 450 °C × 2 h + 460 °C × 2 h +470 °C × 2 h and aging treatment is 120 °C × twenty four h. When the content of Ti varies in the range of 0–0.81 wt%, with the increase of Ti content, the number of undissolved phases increases and dislocation strengthening increases. However, the electrical conductivity of the alloy decreases gradually, and the hardness and room temperature tensile strength first basically remain unchanged and then decrease (the strength of the alloy decreased from 740.05 MPa to 738.5 MPa and then to 700.09 MPa). The elongation of the alloy decreases slightly after fracture, and the intergranular corrosion resistance increases first and then decreases. With the increase of Ti content, the peak stress of hot compression of the alloy increases first and then decreases at 250 °C. Therefore, considering the properties, the optimum composition of the experiment is Al-10.2Zn-2.59Mg-0.92Cu-0.184Zr-0.34Ti. Its room temperature tensile strength is 738.5 MPa, and the elongation after fracture is 7.5%, and the peak thermal compression stress at 250 °C is 357.4 MPa(Increase by 48% compared with Ti-free alloys).

Effects of alloying elements on mechanical and thermal characteristics of Al-6wt-%Si-0.4wt-%Mg–(Cu) foundry alloys

ABSTRACTThe objective of this study was to investigate the effects of alloying elements on mechanical and thermal characteristic of Al-6wt-%Si-0.4wt-%Mg–(Cu) foundry alloys after heat treatment using a universal testing machine and a laser flash apparatus. Solid solution treatment of samples was carried out at 535°C for 6 h before quenching samples in warm water. Artificial ageing treatment was conducted at various temperatures ranging from 180 to 220°C for 5 h. When Cu was added to increase the mechanical strength of Al-6wt-%Si-0.4wt-%Mg alloy, its thermal conductivity decreased. After adding 0.1wt-%Ti to an Al-6 wt-%Si-0.4wt-%Mg-0.9wt-%Cu alloy, ultimate tensile strength (UTS) was improved 18 MPa compared to that of Ti-free alloy at ageing temperature of 180°C. The addition of Ti facilitated the formation of θ′-Al2Cu and Q′-phase, which resulted in increased UTS at room temperature. In the case of Cu-free Al-6wt-%Si-0.4wt-%Mg alloy, adding Ti to the alloy did not affect the UTS.

Strengthening of Al0.15CoCrCuFeNiTix–C (x = 0, 1, 2) high-entropy alloys by grain refinement and using nanoscale carbides via powder metallurgical route

In this study, Al0.15CoCrCuFeNiTix–C (x = 0, 1, 2) high-entropy alloys (HEAs) were produced via powder metallurgy routes, and the microstructural evolution and mechanical properties of the alloys were investigated with respect to the alloys of Ti content. Cr-carbides were formed in the Ti-free alloy, whereas the Ti-containing alloys contained Ti-carbides instead of Cr-carbides because Ti has a higher affinity for C than it does for Cr. Sigma phases were also formed in the Al0.15CoCrCuFeNiTi2-C alloy. The formation of carbides and intermetallic compounds altered the composition and structure of the solid-solution phases. High-energy ball-milling led to the refinement of microstructures to the nanoscale, and the average grain size of the alloys decreased with increasing Ti content because of the grain-boundary pinning effect of TiC. As a result, the Al0.15CoCrCuFeNiTix–C (x = 0, 1, 2) alloys exhibited high strengths of 2047, 2199, and 2877 MPa, respectively.

Influence of solidification conditions and alloying elements Re and Ti on micropores formed during homogenization of Ni base single crystal superalloy

The influence of withdraw rate during directional solidification and elements Re and Ti on the formation of micropores during homogenization in Ni base single crystal superalloy CMSX-4 is investigated by X-ray tomography method. The results show that the number of micropores below 5 μm in sample solidified at 10 mm/min after homogenization at 1300 °C/3 h is greater than that in the case of 6 mm/min. The number of micropores below 10 μm in Re free and Ti free alloys is rather smaller than that of normal CMSX-4 alloy, while the number of micropores between 15 μm and 25 μm in Ti free alloy is relatively greater than that in Re free alloy. The variation of number of micropores is analyzed based on measurement of primary dendrite arm spacing (PDAS) and segregation ratios of alloying elements, the causes are mainly attributed to reverse segregation tendencies of Re and Ti and their remarkable diffusion coefficient difference, the increasing of PDAS also enhances the propensity of micropores formation during homogenization.

Grain refinement and Al-water reactivity of Al[sbnd]Ga[sbnd]In[sbnd]Sn alloys

AlGaInSn alloys were prepared by using traditional casting metallurgy method with different additions of Al5Ti1B grain refiner. Their microstructures were investigated by means of X-ray diffraction (XRD) and scanning electron microscope (SEM) with energy dispersed X-ray (EDX). The Al grains of alloys are refined significantly from 129 μm to 57 μm with increasing Ti content from 0.03 wt% to 0.24 wt%. Many thin dendrites that are a few micrometers thick are observed within Al grains.Al-water reactivities were performed under different water temperatures. The alloy with Ti content of 0.12 wt% shows the maximum H2 generation rate under different water temperatures, which is above 5 times of Ti-free alloy. The H2 yields of alloys drop from 87% to 30% with rising Ti content from 0.03 wt% to 0.24 wt% at the water temperature of 30 °C, but they rise to about 90% when the water temperature is above 50 °C.The growth mechanism of alloys and the effect of grain refinement on Al-water reactivities are discussed.

Enhanced Oxidation Resistance of Mo–Si–B–Ti Alloys by Pack Cementation

As new high-temperature structural materials, Mo–Si–B alloys satisfy several requirements such as oxidation and creep resistance. Recently, novel Ti-rich Mo–Si–B alloys have shown an increased creep resistance compared to Ti-free alloys. However, due to the formation of a duplex SiO2–TiO2 oxide layer, which allows for fast ingress of oxygen, the oxidation resistance is poor. To improve the oxidation resistance, a borosilicate-based coating was applied to a Mo–12.5Si–8.5B–27.5Ti (in at.%) alloy. After co-deposition of Si and B by pack cementation at 1000 °C in Ar, a conditioning anneal at 1400 °C is used to develop an outer borosilicate layer followed by an inner MoSi2 and Mo5Si3 layer. During both isothermal and cyclic oxidation after an initial mass loss during the first hours of exposure, a steady state is reached for times up to 1000 h at temperatures ranging from 800 to 1200 °C, demonstrating a significantly enhanced oxidation resistance.

Titanium as an intermetallic phase stabilizer and its effect on the mechanical and thermal properties of Al-Si-Mg-Cu-Ti alloy

The effect of precipitation of intermetallics on the mechanical and thermal properties of Al-6.5Si-0.44Mg-0.9Cu-(Ti) alloys (in wt%) during various artificial aging treatments was studied using a universal testing machine and a laser flash apparatus. The solution treatment of the alloy samples was conducted at 535°C for 6h, followed by quenching in warm water. The solution-treated samples were artificially aged for 5h at different temperatures ranging from 170°C to 220°C. After the artificial aging treatment, the Al-6.5Si-0.44Mg-0.9Cu alloy (the Ti-free alloy) had a lower ultimate tensile strength (UTS) than the Al-6.5Si-0.44Mg-0.9Cu-0.2Ti alloy. The UTS response of the alloys was enhanced by the addition of Ti, with the maximum UTS showing an increase from 348MPa for the Ti-free alloy to 363MPa for that containing 0.2wt% Ti, aged at 180°C. The Ti-free alloy had a higher thermal diffusivity than the Ti-containing alloy over all temperature ranges. Upon increasing the temperature from 180°C to 220°C, the room temperature thermal diffusivities increased because the solute concentration in the α-Al matrix rapidly decreased. In particular, the thermal diffusivity increased significantly between 200°C and 400°C. This temperature range matched the range of intermetallic phase precipitation as confirmed by differential scanning calorimetry and measurement of the coefficient of thermal expansion. During the artificial aging treatment, the intermetallic phases precipitated and grew rapidly. These reactions induced a reduction of the solute atoms in the solid solution, thus producing a more significant reduction in the thermal diffusivity. As the temperature was increased to above 400°C, the formation of intermetallic phases ceased, and the thermal diffusivity showed a steady value, regardless of the aging temperature.

Martensitic transformation and magnetic properties of Ti-doped NiCoMnSn shape memory alloy

Martensitic transformation, microstructure, and magnetic properties of Ti-doped Ni43−x Ti x Co7Mn43Sn7 (at%) (x = 0, 0.5, 1.0, 2.0, and 4.0) shape memory alloys were investigated. The results show that transformation temperatures of Ni43Co7Mn43Sn7 can be efficiently adjusted by the substitution of Ti for Ni. For example, the martensitic transformation starting temperature (M s) is reduced by about 278 K with 4 at% addition of Ti. Room temperature microstructure evolves from single tetragonal martensite for the Ti-free alloy to dual phases (tetragonal martensite + second phase) with 0.5 at%, 1.0 at%, and 2.0 at% addition of Ti to dual phases (cubic austenite + second phase) for 4.0 at% Ti-doped alloy. The mechanical properties can be obviously improved by adding an appropriate amount of Ti. A noteworthy point is that magnetic-field-induced reverse transformation is observed in Ni39Ti4Co7Mn43Sn7 alloy.

Ferritic oxide dispersion strengthened alloys by spark plasma sintering

Spark plasma sintering (SPS) was used to consolidate a Fe–16Cr–3Al (wt.%) powder that was mechanically alloyed with Y2O3 and Ti powders to produce 0.5 Y2O3 and 0.5 Y2O3–1Ti powders. The effects of mechanical alloying and sintering conditions on the microstructure, relative density and hardness of the sintered oxide dispersion strengthened (ODS) alloys are presented. Scanning electron microscopy indicated a mixed fine-grain and coarse-grain microstructure that was attributed to recrystallization and grain growth during sintering. Analysis of the transmission electron microscopy (TEM) and atom probe tomography (APT) data identified Y–O and Y–O–Ti nanoclusters. Elemental ratios of these nanoclusters were consistent with that observed in hot-extruded ODS alloys. The influence of Ti was to refine the grains as well as the nanoclusters with there being greater number density and smaller sizes of the Y–O–Ti nanoclusters as compared to the Y–O nanoclusters. This resulted in the Ti-containing samples being harder than the Ti-free alloys. The hardness of the alloys with the Y–O–Ti nanoclusters was insensitive to sintering time while smaller hardness values were associated with longer sintering times for the alloys with the Y–O nanoclusters. Pressures greater than 80MPa are recommended for improved densification as higher sintering temperatures and longer sintering times at 80MPa did not improve the relative density beyond 97.5%.

Wear Behaviors of AA 6063 Aluminum Alloys Reinforced with in situ Al3Ti Particles

The purpose of this study was to examine the microstructure and room temperature dry sliding wear performance of AA 6063 aluminum alloys containing up to 2% Ti under homogenized and heat-treated conditions. After casting, homogenizing heat treatment was applied to all produced alloys at 500°C for 2 h. Heat treatment included water quenching after being kept at 500°C for 2 h, and then an aging process was applied at four hour intervals up to 48 hours, at 150°C. The microstructure of the homogenized and aged alloys was analyzed using a scanning electron microscope (SEM). Hardness measurements were carried out using a microhardness test. Wear tests were performed using a ball-on-disc method by measuring the wear scar areas. Results of the wear tests proved that the wear rate decreased in alloys containing Ti. Though aging heat treatment improved the wear resistance of Ti-free alloys, the wear resistance of each of the alloys containing Ti decreased.

Effect of titanium on the ductilization of Fe–B alloys with high boron content

Binary Fe–B alloys with a high boron concentration are hard but brittle. The brittleness is caused by the formation of a cast microstructure which consists of a continuous network of brittle Fe 2B. In the present investigation, we demonstrated that, by alloying with titanium, and particularly with a titanium-to-boron atom ratio of 0.5, a fine and uniform microstructure can be formed. Also, as a result of the microstructural modification, the alloy is improved from being completely brittle (∼ zero elongation) in the Ti-free alloy to a 4% tensile elongation. The preliminary result indicates that additional rolling at 1223 K further enhances the ductility to over 16%.

The effect of surface preoxidation of sintered silicon carbide on its wettability by silver–copper based brazing alloys in vacuo

Abstract The sessile drop method has been used to determine time dependence of contact angle at 850°C in vacuo for Ag–28wt.%Cu, Ag–35wt.%Cu–1.5wt.%Ti and Ag–22wt.%Cu–12wt.%In–2wt.%Ti on pressureless sintered SiC in the as-polished and high temperature preoxidized conditions. Contact angle was independent of time for the Ti-free alloy and was increased from 137 to 161 or 162° by preoxidising the SiC. Contact angle decreased with time when Ti was present typically from 80 to 110° initially to 5 to 20° after 90 min at 850°C, again values being higher for the preoxidised condition. These behaviours are attributed to the effects of preoxidation in replacing the thin amorphous silica film on the polished surface by a thicker crystalline film which retards the action of Ti in promoting the wettability desired for brazing purposes.

Effect of Nitrogen on Formation of Martensite-Austenite Constituent in Low Carbon Steels.

The effect of dissolved nitrogen on phase transformations and microstructural evolution in low-carbon high manganese silicon steel wire-rod was examined for varying nitrogen levels of 30, 70, and 100 ppm, while keeping the base composition constant. It was found that nitrogen suppresses the pearlite reaction start temperature by up to 30°C. A strong correlation was discovered between the nitrogen level and the formation of martensite-austenite microconstituent (MA phase). The possible mechanisms by which nitrogen causes the formation of MA phase are discussed. The main conclusion drawn from this study is that levels of nitrogen between 70 and 110 ppm can have a significant effect on microstructure, such that up to approximately 10vol% of MA phase is formed in these steels. Microstructural changes in titanium-microalloyed steels were also investigated - particularly changes in the development of the MA and pearlite phases. The pearlite content was up to double that found in a Ti-free alloy. Microalloying with titanium was found to be effective in completely eliminating MA phase.

Phase chemistry and precipitation reactions in maraging steels: Part IV. Discussion and conclusions

This article summarizes our studies of phase chemistry and precipitation reactions in a variety of maraging steels. The roles of different phases and alloying elements are investigated by comparing the behavior of different steels. The phases considered are Ni3Ti, Fe7Mo6 μ phase, Fe2Mo Laves phase, ω phase, Ti6Si7Ni16 G phase, “Z phase,” austenite, and α matrix. The alloying elements discussed are Ti, AI, Mo, Si, Mn, Ni, Cr, and Co. By comparing the aging behavior of both commercial steels and model alloys, a major role of Co is confirmed to be the lowering of the matrix solubility of Mo. Of the two main hardening elements in maraging steels (namely, Ti and Mo), Ti is much more active than Mo in the very early stage of precipitation. The main Mo-rich precipitate found in this work was Fe7Mo6μ phase instead of Laves phase. The precipitation of Mo is modified by the presence of Ti. ω phase appears only in Ti-free alloys, especially when aged at a low temperature. The quantity of Ni-containing precipitates and the presence of Cr in the steels change the austenite reversion behavior. Other phases, such as G phase and “Z phase,” contribute to age hardening in different types of maraging alloys.

MOVEMENT AND INTERACTIONS OF DISLOCATIONS IN NICKEL-CHROMIUM ALLOYS

Interactions of dislocations, especially under dynamic conditions, on a single glide plane or from two crossing glide planes were studied in general, and certain dislocation configurations in particular, by means of transmission electron microscopy and diffraction contrast methods. The main findings are:1. Hexagonal dislocation networks are mainly formed by the interaction of dislocations on a single glide plane with Burgers vectors at 120°.2. Like screw dislocations, edge and mixed dislocations can also cross-slip between two glide planes.3. Interactions of dislocations from two crossing glide planes sometimes form long, straight, non-mobile dislocations at the intersections, e.g., Lomer-Cottrell dislocations. However, this non-mobile dislocation does not block, as it is generally accepted, the movement of dislocations on these two glide planes.4: In nickel-chromium alloys containing aluminum and titanium, interactions of superlattice dislocations are more or less similar to those observed in Al-and Ti-free alloys or in disordered solid solutions.