Search

This article briefly introduces the concept of creep properties of additively manufactured (AM) alloys, with a focus on the effects of the characteristic microstructure of AM alloys on creep performance. Relevant post-processing treatment also is discussed, in relation to improved creep performance based on the improvement of AM initial microstructure.

This paper describes a novel process for synthesizing a Ti2AlC/TiC/Al2O3in situ composite. This route utilizes TiO2, carbon, and Al powders as raw materials, and involves high-energy mechanical milling and powder sintering. The Ti2AlC/TiC/Al2O3 bulk in situ composite produced has a phase composition of Ti2AlC–20 vol% TiC–35 vol% Al2O3 with fine Al2O3 particles (size: 0.5–15 μm) embedded in a Ti2AlC/TiC matrix. The Ti2AlC grains exhibit a nanometer scale lamellar structure, and most of the Al2O3 grains contain fine cubic TiOmC1−m precipitates (size: 10–200 nm). The average hardness and bending strength of the composite are in the ranges of 11–12.5 GPa and 380–440 MPa, respectively. Here we have demonstrated that the mechanical performance (mainly hardness and bending strength) of the composite is directly correlated with the size of the Al2O3 particles present in the as-fabricated in situ composite.

To maximize the usage of underground space, there will be more and more engineering projects that will be built above the running tunnels. To ensure the safety operation of the running tunnels, there is a need to predict and control the tunnel deformations. This paper combines the experiences from the construction of underpasses above running tunnels in the soft soil region of Shanghai and discusses the rules of rebound effects of running tunnels due to excavation by FEM numerical simulation. The writer attempts to use the soil unloading Semi-experiential modulus derived from the Shanghai soft soil region experiments, taking into consideration the effects of the load-space relation and the effects of the property of the soil within the rebound zone in reaction to the unload distribution to propose a calculation formula for the rebound effects of running tunnels. The results calculated from the formula are very close to those measured, hence proving that the formula is a simple and practical way to predict tunnel deformations within the same regional projects. (A) This paper was presented at Safety in the underground space - Proceedings of the ITA-AITES 2006 World Tunnel Congress and the 32nd ITA General Assembly, Seoul, Korea, 22-27 April 2006. For the covering abstract see ITRD E129148. "Reprinted with permission from Elsevier".