Deformation Behavior of Bulk Ultrafine Grained Copper Prepared by Sub-Zero Rolling and Controlled Recrystallization

Present study aims to investigate the microstructure evolution and mechanical properties of bulk nanocrystalline/ultrafine grained pure Cu obtained after controlled recrystallization of samples heavily cold-deformed at cryogenic temperature. Microstructural characterization has been carried out by X-ray diffraction analysis and hardness measurements. Mechanical behavior has been investigated by tensile testing. Significant dependence of mechanical property on grain size has been recorded. Present study indicates that conventional rolling at subzero temperature followed by controlled recrystallization may be utilized as an effective method for development of bulk Cu with two- to three-fold improvement in yield strength in comparison to its coarse grained counterpart with moderate ductility and toughness.     

Tensile Strength and Ductility of Al-MT (MT = Fe, Ni) Intermetallic Alloys

In this work, FeAl and NiAl intermetallic alloys were produced by conventional casting using SiC crucibles. Li and Ni elements with 1, 3, and 5% were added to the AlFe intermetallic compound. In the case of NiAl intermetallic, the alloy' composition was based on (Ni₅₅Fe₅)Al with additions of 1, 3, and 5% of Li. After casting, the ingots were homogenized to minimize the thermal vacancy effects. For the AlFe ingots, the annealing treatments were carried out at 300°C during 170 hours. In the case of ALNi alloys, the annealing were performed at 400°C over 144 hours. Mechanical tests were carried out in both as cast and homogenized specimens. The experimental results are displayed as a stress-strain graph. The Li additions improve the percent of elongation and the ultimate tensile strength of the AlFe alloy. Additions of Ni improve the yield strength. In the AlNi intermetallic alloy, the best results were obtained with 5% Li additions. The tensile ductilities in intermetallic systems are improved when a heat treatment is used.     

Characterization, Processing, and Alloy Design of NiAl-Based Shape Memory Alloys

The microstructures and phase transformations in binary Ni-al, ternary Ni-Al-Fe, and quaternary Ni-Al-Fe-Mn shape memory alloys (SMAs) were investigated by light and electron microscopy, electron and X-ray diffraction, and differential scanning calorimetry. The effects of alloying additions (B, Fe, and Mn) on martensite stability, shape recovery, and tensile ductility were also studied. NiAl-based SMAs can be made ductile by alloying with B for enhanced grain boundary cohesion and Fe for improved bulk properties. Iron has the undesirable effect that it decreases the martensite → austenite transformation temperatures (A_p). Fortunately, A_p can be increased by decreasing the “equivalent” Al content of the alloy. In this way, a high A_p temperature of 190°C has been obtained without sacrificing ductility. Recoverable strains of 0.7% have been obtained in a Ni-Al-Fe alloy with A_p temperature of 140°C. Manganese additions (2–10%) lower A_p, degrade hot workability, and decrease room temperature ductility. Good-quality, ductile SMA ribbons have been produced by melt spinning. However, additional alloy design is required to suppress the aging-induced embrittlement caused by Ni₅Al₃ formation.     

Dendritic Microstructure Affecting Mechanical Properties and Corrosion Resistance of an Al-9 wt% Si Alloy

It has been reported that the mechanical properties and corrosion resistance of metallic alloys depend strongly on the solidification microstructural arrangement. The correlation of corrosion behavior and mechanical properties with microstructure parameters can be very useful for planning solidification conditions in order to achieve desired final properties. The aim of the present work is to investigate the influence of dendritic microstructural parameters of an Al-9 wt.% Si alloy on mechanical properties and corrosion resistance. The experimental results establish correlations between secondary dendrite arm spacings (λ₂) and ultimate tensile strength (σ_u), yield strength (σ_y), corrosion potential (E_Corr), and corrosion rate (i_Corr).     

Influence of Tool Geometry in Friction Stir Welding

In this article we highlight the results of a recent study undertaken to understand the influence of tool geometry on friction stir welding (FSW) of an aluminum alloy with specific reference to microstructural development, defect formation, and mechanical response. The welding trials were made on 4.4 mm thick sheets using tools made of die steel and having different diameters of the shoulder and the pin, and the profile of the pin. Throughout the welding operation, the rotational speed, traverse speed, and tool axial tilt were held constant at 1400 rpm, 80 mm/minute, and 0 degrees, respectively. For a shoulder diameter of 20 mm and a pin diameter of 6 mm, the severity of defects in the weld was found to be the least and the resultant tensile strength of the weld was high. For the welds that were made using a tool having a shoulder diameter of 10 mm and a pin diameter of 3 mm the tensile strength of the weld was the least since the degree of defects observed were higher.