Effect of milling duration on the evolution of shape memory properties in a powder processed Cu–Al–Ni–Ti alloy

The present work describes the effect of milling duration on the properties of a powder metallurgy processed Cu–Al–Ni–Ti shape memory alloy employing mechanical alloying. Powder mixtures milled for different durations were sintered in order to investigate the formation of solid solution and evolution of martensitic structure. The idea was to optimize the duration of milling (mechanical alloying) to obtain chemical homogeneity as well as shape memory properties in the processed material without undergoing extensive post homogenization treatment. The martensitic structure was noted to evolve in the powder mix milled for at least 16 hrs, whereas complete transformation to martensite occurred after milling for 40 hrs. Interestingly, the dissolution of alloying elements (to form the β phase prior to the formation of martensite) was noted to complete partially only during mechanical alloying for 40 hrs and remaining during subsequent sintering for 1 hr. The hot pressed compacts of the powders milled for 40 hrs were chemically homogeneous and consisted of fully martensite phase, which is essential for the realization of shape memory properties. They also revealed almost 100% shape recovery at the applied pre-strain levels of 1 and 2%.\ud \ud \u

Effects of Microstructural Features and Test\ud Parameters on the Abrasive Wear Response of an Al-Si Alloy

This article discusses some observations pertaining to the abrasive wear response of an Al-Si alloy as influenced by microstructural features and test parameters (applied load and traversal distance). The wear performance has also been correlated with corresponding changes in mechanical properties (hardness, UTS, and elongation) and morphology (length, diameter, and length/diameter ratio) of microconstituents like Si. Microstructural/morphological alterations in the alloy were brought about through T6 heat treatment involving solutionizing followed by artificial aging for different durations. Heat treatment brought about significant alterations in the morphology (length, diameter, and length/diameter ratio) of Si particles, as was also reflected in terms of microstructural changes. The length of the Si particles decreased while their diameter increased leading to a reduction in the aspect (length/diameter) ratio of the phase in the case of the heat-treated samples compared to the as cast alloy. Decreasing length, rising diameter, and reduction in the aspect (length/diameter) ratio indicates a higher degree of spheroidization of the phase as a result of heat treatment. Increasing aging duration caused the aspect ratio to decrease further. The study suggests increasing wear loss with a rise in the applied load and traversal distance. The heat-treated samples attained improved mechanical and reduced wear loss over the as-cast samples in general, an exception being the elongation wherein the property became comparable to that of the as-cast alloy at aging durations beyond 7 h. Also, aging for 3 h seems to be sufficient to realize the benefit of heat treatment in terms of improvement in the wear behavior and mechanical properties since it leads to the highest hardness, UTS and elongation properties. Aging durations longer than 3 h led to deterioration in the UTS and elongation properties, while hardness and wear loss attained steady-state condition. The wear-related observations have further been substantiated through the characteristics of wear surfaces, subsurface regions and abrasive medium. The operating material removal mechanisms were observed to be capping, clogging, attrition, and fragmentation of the abrasive medium (particles). An interesting inference of the present study is that there seems to be a direct correlation between abrasive wear response and hardness of the alloy, while properties like UTS and elongation produce a mixed influence

Sliding wear behavior of a zinc based alloy compared with a leaded tin bronze.

The present paper deals with the dry sliding wear behaviour of a zinc-based alloy against a stainless steel (grade 304) disc (counterface). The performance of the zinc-based alloy has been compared with that of a conventionally used leaded-tin bronze under identical test conditions. Wear tests have been conducted over a range of pressure and speed.\ud The results revealed that the zinc-based alloy performs better than the bronze over the entire range of speed and pressure. Further, the bronze attained improved wear response at the higher sliding speed. At the lower speed, material ``chipping off'' caused the tests to be stopped beyond a specific pressure in the case of the bronze, while material seizure was observed at the higher speed. The zinc-based alloy attained comparable wear rates at both the speeds, while seizure pressure reduced at the higher speed

Effect of aluminium addition on densification behaviour and microstructural features of P/M processed Cu–TiC composites\ud \ud \ud

The present work is focused on the processing and characterization of Cu–TiC composites. The samples were prepared employing addition of TiC particles to the powder matrix followed by mechanical milling, cold compaction and vacuum sintering. The effects of aluminium addition and the contents of Al & TiC on microstructural features, particle fragmentation, crystallite size, lattice strain, densification behaviour and hardness of the (sintered) samples have been analyzed. The composites consisted of uniformly distributed (fine) TiC particles in the size range of 0.2–1.4 µm and the TiC particles possessed sound interfacial bonding with the copper matrix. Increasing aluminium and TiC contents led to a better chemical homogeneity in the composites. Separate addition of Al and TiC to copper brought about increased hardness. Further, the hardness of the samples increased with the addition of rising aluminium content while a mixed effect of TiC content was noticed. Further, aluminium addition was more effective at a higher TiC content in terms of increased hardness of the samples. Moreover, densification behaviour was affected in a mixed manner in the presence of TiC and Al. Factors responsible for the observed behaviour of the samples have been discussed.\ud \ud \u

Sliding Wear Behaviour of Al-7075 based Metal Matrix Composite: Effect of Processing Parameters

Metal Matrix Composite made from Al-7075 based alloy dispersed with 10% SiC particles through the liquid metallurgy route were evaluated for their sliding wear properties under different loads and for a length of sliding distance. The volume loss and wear rate under different\ud experimental conditions were compared between the following conditions for both the alloy and composite (i) cast (ii) aged (iii) extruded. Attempts have been made to arrest wear of the alloys that experience seizure under the mildest of experimental conditions through the above processing\ud techniques and explain the experimental results through worn surface studies. The extent of success attained through each process has been discussed. It is felt that the cumulative effect of the different processing techniques including composite making, ageing and extrusion can open up new avenues\ud for this alloy system, which in general is not used for wear resistant application