An integral manufacturing process with hot drawing and cold flow forming was proposed for large-diameter seamless steel gas cylinders. The main purpose of this study was to find out the effects of the manufacturing process on the microstructure and mechanical properties of gas cylinders made of 34CrMo4 steel. Two preformed cylinders were produced by hot drawing. One cylinder was then further manufactured by cold flow forming. The experiments were carried out using three types of material sample, namely, base material (BM), hot drawing cylinder (HD), and cold flow-formed cylinder (CF). Tensile and impact tests were performed to examine the mechanical properties of the cylinders in longitudinal and transverse directions. Microstructure evolution was analyzed by scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD) to reveal the relation between the mechanical properties and the microstructure of the material. It is found that the mechanical properties of the 34CrMo4 steel gas cylinders were significantly improved after hot drawing and flow forming plus a designed heat treatment, compared with the base material. The observations of microstructure features such as grain size, subgrain boundaries, and residual strain support the increase in mechanical properties due to the proposed manufacturing process.

In this work, (Au₇₉Ni₁₇Pd₄)₉₆Ti₄ (wt.%) filler alloy was designed and employed to join SiC ceramics. The effects of brazing temperature and soaking time on the microstructure and fracture morphology of joints were investigated. The results show that the joint obtained can be described as SiC/reaction layer/braze/reaction layer/SiC. The reaction layer was composed of TiC and Au (Si, Ti). The wettability of the filler alloy toward the SiC ceramics was analyzed. The braze zone was mainly constituted by Pd₂Si, Ni₂Si, and Au (Ni, Si). A large number of nano-sized TiC particles were distributed within the Au (Ni, Si) layer. The formation mechanism of the braze containing different phases was discussed. The brazing temperature and soaking time had a significant effect on the reaction layer at the SiC/braze interface and TiC particles within the Au (Ni, Si) layer, while they showed a negligible effect on the Pd₂Si and Ni₂Si within the braze. The inherent reason was also clarified in detail. The joint fractography indicated that a good bonding was achieved between the filler alloy and SiC, while joint fracture was primarily induced by the thermal stresses residing after the brazing cycle.

In this work, the DD98M single crystal superalloys were brazed to themselves using a Pd-Si composite filler. The effect of brazing temperature and soaking time on the microstructure and mechanical behavior of the joints was studied. The microstructure and phase constitution in the joint were identified by the SEM and EDS analysis. The results indicated that the joint obtained was constituted by DD98M/zone 2/zone 1/zone 2/DD98M. The zone 1 was primarily made up of the Ni (Pd, Cr, Co) (s.s), Pd₄Si, Pd (Ni, Ti, Al) (s.s) and Pd-rich Ni (Pd, Cr, Co) (s.s), while the zone 2 consisted of the Ni (Pd, Cr, Co) (s.s) and Al₂Pd₅. During the brazing process, increasing the brazing temperature strengthened the fluidity of the liquid filler, which was favorable to eliminating the solidified pores in the brazing seam. Furthermore, a higher brazing temperature would cause the phases in the zones 1 and 2 to be coarsened remarkably. When setting the brazing temperature to 1060 °C, extending the soaking time made the amount of Pd (Ni, Ti, Al) (s.s) decrease, whereas the amount of Pd₄Si increased, because the peritectic reaction between the Pd (Ni, Ti, Al) (s.s) and remnant liquid filler was enhanced. Among the brazing process parameters under investigation, the maximum joint average shear strength obtained reached 338 MPa when the joint was brazed at 1060 °C for 30 min. A ductile fracture mode happened during the shear tests under a joining condition. The work performed can provide valuable data to design the single crystal superalloy brazed joint.

A Ni–17Mo–7Cr-based superalloy was laser surface-modified to improve its tribological properties. Si particles were employed as coating materials. Si melted on the surface of the alloy during the process, triggering the formation of Mo₆Ni₆C carbides and Ni–Si intermetallics. A defect-free coating obtained was mostly made up of primary Mo₆Ni₆C and γ-Ni₃₁Si₁₂, as well as a eutectic structure of β₁-Ni₃Si and α-Ni-based solid solution (α-Ni (s.s)). The volume fraction of hard reinforcements (Mo₆Ni₆C, γ-Ni₃₁Si₁₂, and β₁-Ni₃Si) reached up to 85% in the coating. High-temperature microstructural stability of the coating was investigated by aging the coating at 1073 K for 240–480 h, to reveal its microstructural evolution. In addition, the mechanical performance of the coating was investigated. The nanoscale elastic modulus and hardness of Mo₆Ni₆C, γ-Ni₃₁Si₁₂, and α-Ni (s.s) were characterized using the nanoindentation tests. The nanoscratch tests were performed to measure the local wear resistance of the coating. Lastly, the Vickers hardness distribution across the cross-section of the coating before and after thermal exposure was compared. The work performed provides basic information understanding the microstructural evolution and mechanical performance of laser-induced coatings on Ni-based superalloys.