Advanced Materials Research Vols. 154-155

Abstract: In this paper, results concerning the microstructure of Rene N4 alloy layers produced by laser cladding on oriented CMSX-4 single crystal substrates are presented. The microstructure of the deposits was analyzed in the solidification condition after different temperature/time ageing cycles in order to assess the possibility of improving high temperature strength of laser deposited superalloys. The present work demonstrates that single crystalline deposits of René N4 nickel superalloy can be obtained provided that the deposition direction and the processing parameters are properly selected. The clad layer is perfectly bonded to the substrate and presents no pores or cracks. The deposits grow epitaxially on the substrate, so they inherit its orientation. For laser beam powers and scanning speeds varying between 500 to 800 W and 4 to 12 mm/s, respectively and (001) substrates, the deposited material presents a columnar dendritic structure consisting of arrays of similarly oriented dendrites, separated by subgrain boundaries, forming a single crystal. Heat treatments effective for the dissolution of detrimental phases and for inducing the precipitation of cuboid ’-Ni3Al strengthening phase precipitates in the laser clads were established.

Abstract: As a response to “call for contribution to a numerical problem for 2D columnar solidification of binary alloys” [Bellet et al., Int. J. Therm. Sci., Vol. 48(11)(2009), p. 2013], the macrosegregation in a Pb-18wt.%Sn benchmark casting is numerically studied with a two-phase columnar solidification model developed by the current authors. The studies were done with 2D calculations in response to the call, and a 3D calculation was performed to confirm the consistency with the 2D case. A grid-sensitivity study was done to ensure the reliability and accuracy of the present results. The segregation mechanism due to thermosolutal convection was analyzed and the uncertainties resulting from the inaccurate thermophysical properties, modelling and process parameters are discussed. The numerical model was evaluated by comparison with experiments.

Abstract: As a result of unequal reduction, the sideways movement of the strip at the entry is occurred in in-plane roll-bending process with conical rollers. This will reduce the shape quality of the formed ring. To control the sideways movement, FE simulations with applying unilateral and bilateral guide planes are carried out by employing ABAQUS/Explicit code. The results show that, the strip moves towards the bottom end and scratches with guide plane at the trailing end if applying unilateral guide plane; the sideways movement can be controlled effectively with circularity of 0.993 and maximum deviation ratio of 12.5% for the formed ring if applying bilateral guide planes.

Abstract: During numerical simulation of welding process, the temperature field simulation is fundamental for simulating other issues of welding process, and establishing the heat source model is the most basic work for temperature filed simulation. Based on the analysis and induction of arc welding heat source model used in T-joint welding simulation, points out the existing problems and future development direction of heat source model for T-joint, provides a reference for further research and practical application.

Abstract: The single-wheeled cycle is fashion and convenient, but there are some problems when used, especially the joint that connect to the lead bicycle. Due to the unavoidably collision when using, there will be the cause on joint parts with high stress state of frequent change, which makes the single-wheeled cycle under security problem. In order to get it fully, this paper use the FEM software to model the single-wheeled cycle. Under the different acceleration exert, the stress state of the joint and stress distribution are researched, then recommendations given about the potential safety hazard, joint life, and the suggestions for improvement.

Abstract: A model of heat transfer and solidification of continuous cast has been established, including boundary conditions in the mold and spray zones. A finite difference method was used for the numerical simulation. The model calculates the shell thickness and temperature distributions of the slab real time. The importance effect of non-linear material properties of specific heat and thermal conductivity as well as phase changes during solidification is treated. The adequacy of model has been proved by industrial and experimental data. The model can be applied to solve some practical problems in continuous cast.

Abstract: In this paper, the Fe-based cladding layer was prepared on 42CrMo substrate by laser cladding mixture containing chromium nitride. The effects of chromium nitride on microstructure and property of cladding layer were studied. The experimental results indicate the chromium nitride is unstable during the process of laser cladding. It is very difficult to obtain chromium nitride in the laser cladding layer. However, the addition of chromium nitride in cladding powders could promote the formation of austenite phase, and increase the microhardness of cladding layer. The reason about increasing the microhardness of cladding layer is the formation of little carbide and solution strengthening of nitrogen, not the strengthening from chromium nitride.

Abstract: The Creep Age Forming (CAF) technique has been recently developed and used to manufacture aircraft and aerospace panel components with improved mechanical properties, increased shape stability and reduced fabrication cost. Precipitation hardening, stress relaxation and creep phenomena take place synchronously in the forming process. Significant research work has been carried out over the last two decades and the applications have been expanded. This paper reviews the most recent development of materials and process modeling techniques for this new forming process. Some challenges for future modeling investigation about the novel process are also discussed.

Abstract: Comparing with conventional mechanical shot peening (SP) technique, water cavitation peening (WCP) experiments of Almen strips were carried out on a self-manufactured equipment. The results show that WCP demonstrates a wide range of standoff distance (SD) that from the nozzle to the surface of the object. By measuring the colour changes of the Fuji pressure sensing film, over 110 MPa impacting pressure was detected, which is resulted from the bubbles blasting on the sample surface when the SD is from 65 to 100 mm under 40 MPa of operating pressure. 600 MPa compressive residual stress achieved on the suface of the Almen strips after WCPed for 32 min. The depth of the zone affected by the compressive residual stress is about 100 µm. The highest residual stress appears in the top surface layer, while in case of SP it appears in the subsurface. Compared to SP, WCP is capable to get rather smoother surface and cause less deformation of the testing sheet, simultaneously.

Abstract: Friction coefficient is an important parameter in sheet metal forming especially in hot forming. Friction condition not only influences material flow but also affects the thermal conductivity between blank and tools. In this study, varied friction coefficient is introduced to the hot forming simulation of B-pillar made of ultra high strength steel sheet 22MnB5. Three curves of friction coefficient vs. temperature are investigated. All of the heat transferred by conductivity, radiation and convection are considered in the simulation. And the temperature-dependent material and process parameters are supplied. It is demonstrated that the coupling effect among the strength and hardness of the metals, the properties of the oxide film covering blank surface and viscosity of the lubrication oil leads to the fact that the friction coefficient changes with temperature instead of constant during hot forming. The friction coefficient curve characterized by increasing first then decreasing gives the best simulation results and then is followed by the one which is characterized by decreasing first then increasing. The constant friction coefficient is the last.