Stability of rolling texture during heat treatment in a two-phase Ti3Al base intermetallic alloy

The stability of hot rolling texture developed in the ₂ phase of a two-phase Ti₃Al base intermetallic alloy, during subsequent heat treatment, has been systematically investigated. The basal hot rolling texture remains rather stable during recrystallization annealing at temperatures within the single phase ₂ range. Grain growth after recrystallization produces extra orientations other than the basal. For the material with a starting basal texture, heat treatment in the upper ₂, (₂+β) or β phase fields does not change the basic character of the texture, although the sharpness and especially the width of the basal component increase to some extent with the increase in the heat treatment temperature. Heat treatment of material with starting non-basal texture in the upper ₂, (₂+β) or β phase fields does not produce any basal component irrespective of the heat treatment temperature. When the starting material is reasonably strain free and possesses a weak basal texture, heat treatment in the upper ₂, (₂+β) or β phase fields helps in intensifying the basal component to a certain extent.     

Thermoelectric performance of p-type Bi–Sb–Te materials prepared by spark plasma sintering

In the present study, p-type (Bi,Sb)₂Te₃ thermoelectric materials have been fabricated through the spark plasma sintering (SPS) method by using powders with various particle sizes. Electrical conductivity (σ), Seebeck coefficient (), and thermal conductivity (κ) were evaluated in the temperature range of 300–500 K. The effect of annealing of the sintered samples on thermoelectric properties was also investigated. The maximum figure of merit ZT (ZT = ²σT/κ) of the sintered samples in the direction perpendicular to the pressing direction (with c-axis preferred orientation) was 1.15 at about 350 K, corresponding to be about 115% of that of the zone-melted ingot with the same composition in the same crystallographic orientation; while the bending strength was highly improved from about 10 to 80 MPa.     

Investigation of the influence of thermal treatment on the morphologies, dielectric and ferroelectric properties of PZT-based ceramics

Pb[(Zr_1/2Ti_1/2)_0.9(Zn_1/3Nb_2/3)_0.1]O₃ (PZT–10PZN) powder was prepared using the columbite precursor method. The phase development of calcined powder precursors was analyzed by X-ray diffraction. Dielectric and ferroelectric properties of the as-sintered and annealed samples were measured and correlated with the microstructure. The morphological evolution was determined by scanning electron microscopy (SEM). The as-sintered ceramic exhibited weak normal-ferroelectric behavior, with a relatively low dielectric constant maximum measured at 1 kHz (_rmax at 1 kHz) of 13,000. Annealing resulted in a transition to relaxor-ferroelectric-like behavior, a shift in the dielectric maximum temperature from 360 to 350 °C, and a dramatic increase in _rmax at 1 kHz to a maximum value of 35,000 for the longer anneal. Furthermore, after thermal annealing at 900 °C for 1 week the composition shifted close to the MPB with a great reduction in the transition temperature and a broadening of the dielectric constant maximum. A strong enhancement of the remanent polarization (P_r) was also observed.     

Another unusual phenomenon for Zr7Ni10: structural change in hydrogen solid solution and its conditions

Zr₇Ni₁₀ has three hydrogen occlusion phases, , β and γ, and the following unusual features are known for the phase transitions in the Zr₇Ni₁₀–H₂ system: (1) The intermediate hydride phase (β) appears only during dehydrogenation but not during hydrogenation, and (2) The continuous hydrogen solid solution phase () exhibits a much higher hydrogen solubility during hydrogenation than during dehydrogenation. In order to clarify the mechanism about the difference in the hydrogen solubility of the phase, the relation between the pressure-composition isotherms and corresponding structural change has been examined by a conventional volumetric method and X-ray diffraction. Through the examination, we discovered that the crystal structure of the phase, which undergoes hydrogenation followed by dehydrogenation, is different from that of its pure metal phase, where the crystal structure of the dehydrogenated phase changes from an orthorhombic structure to a tetragonal structure. The conditions causing the structural change were then examined, and it has been found that the phase maintains its original orthorhombic structure as long as it is hydrogenated so as not to absorb enough hydrogen to change it to the hydride with a higher hydrogen content (γ). The phenomenon can be understood as one of the hydrogen-assisted phase transitions such as hydrogen-induced amorphization (HIA) in the sense that the phase transition requires hydrogenation under special conditions.     

Direct laser fabrication of nickel alloy samples

Direct laser fabrication (DLF) is an advanced manufacturing technology which can build full density metal components directly from CAD files without using any modules or tools. An open-loop controlled hardware system and associated control software for the DLF process of nickel alloy samples was constructed in our work. The hardware system is consisted of a CO₂ laser, a 4-axis CNC table, a coaxial powder nozzle and a powder recycler. In order to achieve the maximum flexibility and extensibility for the fabrication of metal parts, path plug-ins was introduced into the control software. The effect of the specific energy on the cross-section shape of nickel alloy cladding was studied by a single-track cladding experiment with different laser processing parameters. The comprehensive effect of the optimized laser processing parameters was also studied by an orthogonal experiment. The experimental results showed that the specific energy for laser processing is the most important factor, which controls the component qualities. There is an appropriate range for the specific energy in which the nickel alloy samples can be fabricated layer by layer with a uniform height. If the specific energy is too low, the inner height of a sample is lower than its contour height. Banding structure can be observed in the microstructure of nickel alloy samples. The gain size in the light zones of the bandings is much smaller than those in the dark zones.     

Corrosion characteristics of plasma-sprayed Ni-coated WC coatings comparison with different post-treatment

The effects of vacuum annealing and laser remelting on the microstructure and corrosion behaviour of plasma-sprayed Ni-coated WC coatings on steel substrate have been investigated. The laser remelting was operated in a continuous way while the vacuum annealing was operated with clamping the coating on the graphite face in order to avoid decarburization of WC. When compared with the as-sprayed coating, the microstructure of the post-heating treatment coatings has been found to consist of different phases. Moreover, the denser microstructure can be obtained after heating treatment, especially the laser remelting coating. Electron probe micro analyzer (EPMA) shows that the chemical composition remained largely unchanged except the “bumps” at the interface for as-sprayed and vacuum annealing coatings. The more uniform composition was obtained for laser remelting coating. The Vickers microhardness measurement shows a very slightly enhancement for post-heating treatment coatings, which may be duo to the lamellar structure, lower contemt and bulky of carbide for coatings. However, salt spray corrosion (SSC) show the laser remelting coating has the best corrosion resistance, which is due to its low number defects and uniform distribution of the phase and composition.     

Effect of Different Scale Precipitates on Corrosion Behavior of Mg–10Gd–3Y–0.4Zr Alloy

A large amount of directional and willow-like β' phase was precipitated in Mg-10 Gd-3 Y-0.4 Zr(GW103 K) alloy after solution treatment and subsequently aged treatment(T6). In order to explore the effect of the precipitates on the corrosion behavior of the GW103 K alloy, the alloy was subjected to solution treatment(T4) at 773 K for 4 h at first, subsequently aged at 498 K for 193 h(T6). The microstructure evolution of the GW103 K alloy after this treatment was investigated by scanning electron microscopy and transmission electron microscopy. The high-angle annular detector dark-field scanning transmission electron microscopy was used to observe the typical corrosion morphologies of the nanoscale precipitation phases(β') in the T6-treated alloy. The corrosion rate was measured by potentiodynamic polarization test. Combining with the potential measurement results by scanning Kelvin probe force microscopy, the effects of the skeleton-like Mg_(24)(Gd,Y)_5 andf precipitates on the corrosion behavior of GW103 K alloy were explored. The results showed that the corrosion rate of the GW103 K alloy in different conditions was ranked as: as-cast alloy T4-treated alloy T6-treated alloy,attributing to the fact that the relative potential differences of skeleton-like Mg_(24)(Gd,Y)_5 were lower than those of the matrix, therefore Mg24(Gd, Y)5 phase formed micro-galvanic coupling with the matrix and corrosion dissolution occurred.The nanoscale β' precipitates in T6-treated alloy can retard the cathodic process.     

Improved Corrosion Resistance of Selective Laser Melted Ti–5Cu Alloy Using Atomized Ti–5Cu Powder

The different types of metal powder used for selective laser melting(SLM) process would cause distinct corrosion behavior due to the uniformity of the obtained microstructure.The SLM-produced Ti–5Cu alloy using atomized Ti–5Cu metal powder(SLMed Ti–5Cu) in this work reveals a relatively uniform microstructure with overwhelming acicular α/α′ phase and shows great advantages on corrosion resistance compared with the SLM-produced Ti–5Cu alloy using the mixture powder(SLMedM Ti–5Cu).The effect of the micro-galvanic cells decreases due to the undetectable Ti_2Cu phase in the microstructure of the SLMed Ti–5Cu.An apparent passivation behavior was observed for SLMed Ti–5Cu instead of severe pitting phenomenon for the SLMed-M Ti–5Cu.The charge transfer resistance of SLMed Ti–5Cu in this work is 10.09 ± 2.63 MΩ cm~2, which is significantly higher than that of SLMed-M Ti–5Cu(4.76 MΩ cm~2).The above result indicates the atomized Ti–5Cu powder plays an important role in the formation of the uniform microstructure of SLMed product, thereby enhancing its corrosion resistance in Hank's solution at 37 ℃.     

激光选区熔化TC4合金工艺优化及退火处理对显微组织的影响研究

激光选区熔化技术是制备复杂钛结构的重要加工方式,而热处理是必要的后处理手段。首先利用激光选区熔化设备打印TC4合金块体结构,以激光功率、扫描速度及扫描间距为优化对象,以致密度为优化目标开展正交试验,得到成形工艺参数对致密度的影响排序及最优工艺参数。然后对最优工艺参数下的成形样件分别进行消除应力退火处理与完全退火处理,发现消除应力退火前后组织改变较小,而完全退火热处理使微观组织从亚稳态的α′相转变成了α+β相稳定组织,这使拉伸试样在完全退火处理后抗拉强度与屈服强度都有所降低,而延伸率大幅提高。