Effect of Niobium on the Microstructure and Mechanical Properties of Alloyed Ductile Irons and Austempered Ductile Irons

In this research, different ductile irons and austempered ductile irons were successfully developed using several alloying contents of nickel, copper and microalloying with niobium. Additionally, special nanocarbon powder was added to the molten iron to enhance the nucleation tendency of spheroidal graphite and compensate for the possible negative effect of Nb addition on the nodule morphology. Metallographic analysis showed that increasing the niobium content in the alloy to 0.1 wt % raises the number of graphite eutectic cells and refines the final structure of the graphite. Moreover, the nodule count of graphite slightly increased, but it concurrently decreased the nodularity when the Nb amount reached 0.1 wt %. SEM micrographs illustrated that nano- to microsized niobium carbides (NbC) particles were dispersed in the matrix of the Nb microalloyed ductile irons. Both optical and SEM micrographs clearly showed that alloying of ductile irons with nickel, copper and microalloying with niobium had a significant effect on defining the final pearlite structure. Coarse, fine, broken and spheroidized pearlite structures were simultaneously observed in all investigated alloys. Dilatometry studies demonstrated that the nano NbC particles acted as nucleation sites for graphite and ferrite needles. Therefore, Nb addition accelerated the formation of ausferrite during the austempering stage. Finally, alloying with Cu, Ni and microalloying with Nb led to developing novel grades of ADI with excellent strength/ductility property combination.

Study the Ductility of Aluminum Alloy Processed by Asymmetric Rolling Process

Asymmetric rolling refers to the conditions wherein velocities or diameters of two work rolls are different. Compared to symmetrical rolling, asymmetric rolling is more effective on microstructure modification and texture evolution. Intense shear deformation can be introduced into asymmetric rolling to enhance the ductility and formability of aluminum alloy and this is the aim of current research. The process of the asymmetrical rolling was done on specimens with different reductions (10%,15%, and 20% reductions). Then the tensile test was conducted at room temperature at the strain rate range between 0.33×10-3s-1 - 3.33×10-3s-1 to study the ductility property of the asymmetric rolling-deformed samples and also compared with as-received samples. The results show that the as-received specimen gave the highest elongation of 42.7%, while the lowest elongation of 22.4% was obtained by the (20%) thickness reduction specimen. Also, the as-received sample at an initial strain rate of 3.33×10-3s-1 gives the highest tensile strength value equal to 550MPa.

Hexagonal Closed-Packed Precipitation Enhancement in a NbTiHfZr Refractory High-Entropy Alloy

A NbTiHfZr high-entropy alloy (HEA) with a main phase of body-centered cubic structure is fabricated. Some hexagonal closed-packed (hcp) precipitates are observed in this alloy. A thermal-mechanical process, i.e., cold-rolling followed by annealing, can manipulate the volume fraction of the hcp nano-precipitates that can enhance strength and ductility. The enhancement is tailorable as a function of the volume fraction of the hcp nano-precipitate. The results indicate that the strength-ductility property can be manipulated via adjusting post-deformation heat-treatment methods, which provide a new strategy by utilizing metastability at high-temperature to design high strength refractory HEAs (RHEAs) without lost in ductility.

Optimization Research on the Corrugated Web of H-Beam with Trapezoidal Webs

Based on the theory study of stress characteristics of the H-beam with corrugated web under transverse load, optimization analysis was conducted. The optimization analysis focused on the corrugation configuration of web, by which one optimized dimension was put forward. To verify the optimization result, total 10 specimens are tested. From the results, the optimization configuration can provide relatively high shear strength and ductility property, with low steel usage. So it can be put into production practice.

Experimental Research on Seismic Behavior of Strengthened R.C. Frame with Special-Shaped Columns

In this paper, a damaged R.C. frame with special-shaped columns has been strengthened for earthquake resistance. The strengthening method combines wrapping steel outside and stick steel. The experimental research on seismic behavior of the strengthened frame was performed. Through the quasi-static test, the load-displacement hysteretic curves under horizontal low-cycle loading are given, and the failure modes of the strengthened frame structure are summarized. This paper gives the analysis of its bearing capacity, stiffness deterioration, energy dissipation capability and ductility property. After comparing the strengthened frame with that before damaged, we draw a conclusion that the method of seismic strengthening in this paper can effectually improve the carrying capacity of damaged R.C. frame with special-shaped columns, and make the strengthened frame have better ductility.

Time-Dependent Ductility of Electro-Deposited Copper

Mechanical ductility property of copper deposits is one of the most important factors necessary to provide a reliable component for the flexible printed circuit boards. Copper deposits are usually fabricated by either an electroless technique or an electrode position process. Among many parameters controlling the deposits quality, it is believed that the current density, bath temperature, the film thickness, annealing temperature and time, and the presence of impurities exhibit particularly strong influences on the mechanical ductility property. In our preliminary studies, it was found that the ductility obtained by the mechanical bulge testing showed a three-stage characteristics in terms of a room temperature annealing; namely (i) initial low ductility regime (from the right-after-copper-deposition until 12 hours aged at room temperature), (ii) transitional rapid increasing ductility regime (from 12 hours to 24 hours), and (iii) the high ductility regime (after 24 hours). In this study, X-ray diffraction analyses of the diffracted line width, the microstrain from which the dislocation density was estimated, residual macrostress, and the scanning electron microscopic observations were conducted and results were correlated with the characteristic three-stage ductility change behavior described above. Results of this study indicate that grain size and residual stress changes are strongly associated with improvement in copper ductility during the room temperature annealing.