Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-31 Cooperative journals: 《中国腐蚀与防护学报》
Abstract： Three high- entropy alloys Co1.5CrFeNi1.5Ti0.5Mo0.1, AlCoCrFeNiSi0.1 and TaNbHfZrTi were prepared by arc melting. Their phase structure, microstructure and chemical composition were studied by means of X-ray diffraction (XRD) and scanning electron microscopy (SEM). A commercial alloy 690TT was used as the contrast material. The repassivation kinetics of the three high entropy alloys in high temperature pressurized water was investigated by means of electrochemical test. The results show that Co1.5CrFeNi1.5Ti0.5Mo0.1, AlCoCrFeNiSi0.1 and TaNbHfZrTi high entropy alloys are all composed of single phase. The crystallographic structure of Co1.5CrFeNi1.5Ti0.5Mo0.1 alloy is fcc, while that of the alloys AlCoCrFeNiSi0.1 and TaNbHfZrTi is bcc. The SEM results show that the Co1.5CrFeNi1.5Ti0.5Mo0.1 alloy showed a typical dendritic microstructure, of which the dendrite riches in Cr and Fe, but the interdendrite zone riches in Ti and Ni. There is no obvious element segregation observed in the AlCoCrFeNiSi0.1 alloy. The TaNbHfZrTi alloy also exhibited a dendritic microstucture, of which the dendrite riches in Ta and Nb, and the interdendrite zone riches in Hf, Zr and Ti. The repassivation rates of these four alloys in high-temperature pressurized water may be ranked as the following sequence: TaNbHfZrTi＞Co1.5CrFeNi1.5Ti0.5Mo0.1＞690TT＞AlCoCrFeNiSi0.1.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-31 Cooperative journals: 《腐蚀科学与防护技术》
Abstract： A novel chromium-free titanate- zirconate conversion coating on 2024 aluminum alloy was prepared, the corrosion resistance of the coatings was evaluated by means of potentiodynamic measurement, NSS test and AC impedance spectra. The morphology and composition of the coatings were characterized by means of SEM with EDS. The results showed that the titanate – zirconate conversion coating is made up of micro particles and shows a smooth flat surface with a few defects. After NSS test for 168 h, only a little corrosion products can be observed on the surface of the titanate- zirconate conversion coating on 2024 aluminum alloy, implying that the conversion coating possesses passivation ability to a certain extent. Therefore, the prepared chromium-free titanate-zirconate conversion coating can provide excellent corrosion protection for 2024 aluminum alloy efficiently.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-31 Cooperative journals: 《腐蚀科学与防护技术》
Abstract： Cold galvanizing coatings were prepared. The coating properties were characterized by salt spray test and electrochemical impedance spectroscopy. Among others, the coating with 95.2% (mass fraction) Zn exhibits the highest corrosion resistance to salt spray, and its corrosion product consists of ZnO and Zn(OH)2. When the Zn content is less than 75%, the impedance of coatings in the solution of 3%(mass fraction) NaCl decreases with the increasing immersion time, and thus the coatings provide inferior protectiveness; when the Zn content is greater than 75%, the impedance of the coating decreases firstly and then increases with the increasing time, which may be ascribed to that the Zn powder in the coating acts as sacrificial anode，which was preferentially corroded in the initial statge.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-31 Cooperative journals: 《材料研究学报》
Abstract： Pre-alloyed powders of T55 have been hot-isostatic-pressed (HIPed) at different HIPing temperatures, and the powder compacts were solution- and aging- treated. Thereafter the powder compacts were carefully examined to establish the relationship between their microstructure and mechanical property. Powder compacts HIPed at 940℃ and 970℃ showed no significant difference on the microstructure and tensile properties. Due to the densification wave effect caused by a non-uniformity of temperature/pressure field during HIPing, the recommended HIPing temperature is 940℃ in this work. The tensile property of powder compact at 600℃ was improved obviously after solution- and aging- treatment. The tensile property of the heat-treated powder compact is close to that of the wrought alloy but better than those of the cast ones. Finite element analysis was used to predict the final dimensions of the small casing component after HIPing, which is well consonant with the experimental data, thus, the FEM analysis is an efficient method for the design and manufacture of powder components. Based on the optimal container design and FEM analysis, a large thin-wall cylindrical structure of Ti55 alloys was manufactured successfully.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-19 Cooperative journals: 《金属学报》
Abstract： With the fast development of industry, pollution becomes a very serious problem. The industrial and life wastewater are discharged and cause the environment pollution. Supercritical water oxidation (SCWO) becomes the most effective method to treat the wastewater. But the material used in the equipment plays a key role in restricting the application of the SCWO process. Currently, during the SCWO wastewater treatment process, 304 austenitic stainless steel, Alloy 625, P91 and P92 steels are the main preheater and reactor materials. In order to reduce the serious corrosion and improve economic efficiency of the materials for this process, a new corrosion resistant Ni-based alloy X-2# alloy has been developed with an aim of replacing the previous ones. In particular, it is highly important to the related behavior of this new alloy welding with the original SCWO. Therefore, the microstructure and mechanical properties of the welding joint of the new alloy and alloy 625 with manual argon arc welding were investigated. The microstructure and fracture morphologies of the welding joint were analyzed by OM, SEM and EDX. The micro- hardness, tensile strength and other mechanical properties were tested and analyzed. The results indicated that more isometric crystals in remelting zone to improve the welding seam strength and the microstructure in fusion zone of X-2# side did not show welding defects. However, some NbC and Laves phases formed near the fusion zone of 625 alloy sides, which affected the mechanical properties of material. Due to the influence of two thermal cycles near the remelting zone, the grains of heat affected zone (HAZ) were easy to grow. But the thermal stability of X-2# side HAZ could reach excellent level. Fine grains of 625 parent material led to grain growth seriously in HAZ, which reduced its Vickers hardness. Because of the tensile strength of welding joints of room temperature and 500 ℃ was lower than the parent materials, the welding seam could be the weakest link. The tesile fracture of X-2#/625 dissimilar metal welding joint was dimple morphology.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-18 Cooperative journals: 《材料研究学报》
Abstract： Pre-alloyed powders of Ti-47Al-2Cr-2Nb-0.15B (%, atom fraction) were prepared by an electrode induction melting gas atomization process, and powder metallurgy (PM) γ-TiAl alloys were prepared by hot isostatic press (HIP). Pre-alloyed powders of γ-TiAl were characterized. A comparison study was made between vacuum degassed and not degassed for the pre-alloyed powders and the PM alloys were subjected to tensile and rupture life test at different temperatures. Infrared spectrum analysis showed that the powders would absorb H2O when exposed in air. By getting rid of the absorbed H2O and O2 through a carefully designed vacuum degassing pre-treatment, the numbers of voids in the prepared PM γ-TiAl alloys decreased obviously, correspondingly the rupture life, as well as the consistency of room temperature tensile elongation, was also improved. In order to find out the influence of container materials on the microstructure and mechanical properties of the PM γ-TiAl alloys, two different container materials (CP-Ti and mild steel) were adopted. Experimental results showed that a lot of obvious voids appeared in the reaction zone due to severe reaction diffusion between the mild steel container and the PM γ-TiAl alloys when HIPed at 1260oC. The shielding effect of the mild steel container was stronger than that of the CP-Ti container, thus the densification shrinkage process of the CP-Ti canned PM γ-TiAl alloys would be more fully completed when HIPed at 1230oC compared with that of the mild steel canned PM γ-TiAl alloys, and thereby both of the yield and tensile strength were both improved. The γ-TiAl alloys prepared by powder metallurgy route present more uniform microstructure, finer grain and better properties compared with the casting alloys. Furthermore, the PM γ-TiAl alloys had no texture which was very common for the casting alloys.
Subjects: Materials Science >> Materials Science (General) submitted time 2016-11-15 Cooperative journals: 《金属学报》
Abstract：本文采用高分辨透射电镜(HRTEM)和原子探针层析技术(APT)等分析手段研究了一种多相强化型马氏体时效不锈钢时效过程中的元素偏聚特征及其与材料力学/耐蚀性能的关系。结果表明，实验钢在时效过程中析出三种强化相，即富Mo的R′相、Ni3Ti金属间化合物η相和富Cr的α′相，其中R′相与η相一起形成核壳状结构，α′相则单独弥散分布于基体中。时效时间延长至40h后，主要强化相η相的成分、数量密度和等效半径基本稳定，同时实验钢的强度不再发生明显的变化，这种优异的抗过时效能力得益于主要强化相形成的核壳状结构。腐蚀试验结果表明，由于富Cr的α′相的析出，导致了贫Cr区的形成，进而降低了实验钢的耐蚀性能。
Subjects: Materials Science >> Materials Science (General) submitted time 2016-11-04 Cooperative journals: 《金属学报》
Abstract：通过对一种新型镍基耐蚀合金U26-2#与625合金手工氩弧焊接接头拉伸性能和硬度的测试，并结合OM，SEM和EDS分析等手段研究了焊接接头的组织和性能。结果表明，U26-2#/625异种金属焊接焊缝重熔区等轴晶组织增多，有利于提高焊缝区强度。U26-2#合金一侧熔合区组织过度良好，而625合金一侧晶界有NbC和Laves相析出，影响材料的力学性能。热影响区在靠近重熔区附近的晶粒由于受2次热循环的影响，出现晶粒长大现象，而U26-2#合金一侧热影响区的热稳定性较好。625合金母材晶粒细小导致其热影响区晶粒长大明显，从而使625合金一侧热影响区的维氏硬度值降低。U26-2#/625焊接接头在室温到700 ℃下的抗拉强度均低于2侧母材，焊缝区为接头最薄弱环节，断口形貌均为韧窝状的韧性断口。
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