The durability of atmospheric plasma-sprayed thermal barrier coatings (APS TBCs) with a double-layer bond coat was evaluated via isothermal cycling tests under 1120 °C. The bond coat consisted of a porosity layer deposited on the substrate and an oxidation layer deposited on the porosity layer. Two types of double-layer bond coats with different thickness ratios of the porosity layer to the oxidation layer (type A: 1:2 and type B: 2:1, respectively) were prepared. The results show that the porosity layer was oxidation free, the oxidation layer included a fraction of well-distributed α-Al₂O₃. The coefficient of thermal expansion of the oxidation layer was about 11.2 × 10⁻⁶ K⁻¹, which was rather lower than that of the porosity layer. Thus, the oxidation layer can be regards as a secondary bond coat between ceramic topcoat and traditional bond coat. The thermal cyclic lifetime of type A TBCs was about 60 cycles, which exceeded 1.2 times the durability of type B TBCs. The delamination cracks in both TBCs all propagated in the ceramic topcoat, which were all identical to those in traditional TBCs. Therefore, the design of the double-layer bond coat affected the stress level rather than the stress distribution in TBCs.

An unstable assembly gap is detrimental to the formation and performance of the pipeline butt girth weld joint. Therefore, a numerical model of an 18.4 mm-thick X80 pipeline girth weld by a homogeneous body heat source was established to investigate the effect of the butt gap on the joint temperature and stress field, and carrying capacity. The accuracy of the simulation results was verified by measuring the welding thermal cycle with a thermocouple. The investigation results showed that the weld pool, heat-affected zone (HAZ) width, and maximum circumferential stress of the joint rose with the increase in the butt gap. The tensile stress unfavorable to the joint quality was mainly distributed in the weld metal and partial HAZ, and the distribution areas gradually expanded as the gap increased. The Von Mises stress peak value of the joint appeared in the order of 3 mm > 2 mm > 1 mm > 0 mm gap, reaching the maximum of 467.3 MPa (3 mm gap). This variation trend is directly related to the improvement in welding heat input with increasing butt gaps. The maximum Von Mises stress of the joint was positively correlated with the carrying capacity of the pipeline, which diminished as the butt gap enlarged. The pipeline carrying capacity reached 17.8 MPa for the joint with no butt gap, and dropped to 13.1 MPa for the joint with a 3 mm gap. The relationship between the carrying capacity (P) and butt gap (C) was described by P = −0.125C² − 1.135C + 17.715, through which the pipeline carrying capacity with other butt gaps can be predicted.

A novelty Al matrix composite reinforced with Cr₃C₂ particles was prepared by an ultrasound vibration treatment-assisted casting process. The Cr₃C₂ content on the microstructure and mechanical properties of Cr₃C_2p/Al composite were researched systematically. The results indicated that Cr₃C₂ particles were effectively distributed around the grain boundary and led to a great reduction in crystalline size. The density, porosity, and Vickers hardness of the composites rose simultaneously with the increase of Cr₃C₂ content. Meanwhile, the tensile strength and yield strength increased by 104.5% and 85.7%, respectively by adding 3.0 wt. % Cr₃C₂. The fracture morphologies showed that the fracture mechanism was plastic fracture for the pure Al and gradually transformed to brittle fracture as the content of Cr₃C₂ exceeded 3.0 wt. %. Moreover, the strengthening mechanism of the composite was also discussed.

High-temperature corrosion severely impairs the service life of boiler heating tubes and threatens the safe and economical operation of thermal power units. With diversified fuels (coal, biomass and refuse-derived fuels) and continuously elevated operating parameters (steam temperature exceeding 620 °C for ultra-supercritical units), boiler heating surfaces are exposed to increasingly complex corrosive environments. High-temperature oxidation, sulfidation, chlorination, molten salt hot corrosion and deposit-induced multi-factor coupled corrosion coexist and exacerbate each other. This paper adopts a four-dimensional analytical framework of “mechanisms–technologies–materials–evaluation” to systematically summarize relevant research progress. From the perspective of corrosion mechanisms, the evolution of understandings from single high-temperature oxidation to multi-factor coupled corrosion is reviewed. In terms of surface coating technologies, seven mainstream processes including HVOF/HVAF spraying, plasma spraying, cold spraying, laser cladding and weld overlay are compared in terms of preparation characteristics and engineering applicability. For coating materials, twelve material systems such as NiCr alloys, MCrAlY, cermets, Fe-based amorphous/nanocrystalline alloys and high-entropy alloys are evaluated for their corrosion resistance under diverse service conditions. As for monitoring and evaluation, this work introduces full-range corrosion management technologies covering electrochemical monitoring, non-destructive testing, numerical simulation and life assessment. Finally, the paper discusses the application prospects of gradient coating design, AI-assisted material screening and digital twin technology, and points out key research gaps including long-term service reliability verification of coatings and quantitative prediction models for multi-factor coupled corrosion.

The effect of the morphology of the wax on the flow state in the coiled tubing with concentric cable was studied by numerical simulation. The results show that flow stream lines of crude oil are parallel to each other in the tubing with no waxing. It is disturbed at the two ends of wax deposition, transvers flow is formed at ends of wax and flow oil is speeded up in gap between wax and cable, friction pressure loss is then increased. This kind of influence becomes more serious with the increase of wax deposition proportion and thickness. An equivalent thickness is proposed to incorporate the influence of wax deposition proportion, length and thickness. With this parameter, a model is developed to calculate the pressure loss induced by wax on the base of concentric model, which can be used conveniently in engineering.

A novel method has been proposed to prepare porous materials through deposition of semi-molten particles by flame spraying. In this study, it was found that the porous material was deposited by the stacking of semi-molten particles which were welded by the molten fraction to form a large and strong inter-particle bonding neck between deposited particles. In order to reveal the effect of inter-particle bonding on the compressive behavior of porous Mo, the deposits were investigated by altering the bonding through vacuum sintering of porous Mo with different porosities. Results showed that the sintering temperature and time influenced the bonding significantly and subsequently influenced the properties of flame-sprayed porous Mo deposits. The oxides formed during flame spraying were effectively reduced under hydrogen atmosphere. In addition, the inter-particle bonding and compressive properties of flame-sprayed porous Mo were significantly improved by optimizing the sintering temperature and the heat treatment time.