Gaurav Kumar Gupta

Effect of milling parameters on processing, microstructure and properties of Cu-Al-Ni-Ti shape memory alloys

The effect of milling parameters, such as ball/powder ratio (BPR), milling speed and time, on the microstructural and phase development of powder metallurgy processed Cu–Al–Ni–Ti shape memory alloys has been studied. It has been found that milling for 40 h at a BPR of 40:1, 200 rev min-1 is the optimised condition for mechanical alloying in an attritor mill in order to get a uniform distribution of the alloying elements. A lower BPR caused insufficient milling, whereas a higher BPR led to oxidation of the powder. The complete formation of martensite occurred in the sample prepared under the optimised milling condition followed by cold compaction, sintering at 900°C for 1 h in vacuum and finally quenching. The austenite transformation temperature of the prepared shape memory alloy was found to be ∼208°C. Thus, the developed process enables to curtail the long milling time as well as decrease the prolonged homogenisation treatments.

Effect of separate and combined milling of Cu and TiB2 powders on the electrical and mechanical properties of Cu–TiB2 composites

ABSTRACT The present work compares the properties of the Cu–TiB2 composites prepared by varying the mechanical milling conditions. The Cu–TiB2 composites were processed using Cu–TiB2 powders combined milling, a powder mixture consisting of separately milled Cu & TiB2 and a powder mixture prepared by the combination of separate and combined milling. The hardness and flexural strength of the combined milled powders were found to be maximum, despite of their lower sintered density. The separately milled powders achieved excellent electrical properties combined with moderate hardness and flexural strength. The properties of composites processed using the combination of separate and combined milling laid in between the two conditions of combined and separate milling.

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

Abstract 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%.

Titanium Foams Processed Through Powder Metallurgy Route Using Lubricant Acrawax as Space Holder Material

Abstract In the present work titanium foams have been synthesized using acrawax as the space holder material. Acrawax has generally been used as a lubricant for easier compaction of aluminium alloy powders. This study deals with the use of this space holder material in the form of beads for creating pores in titanium metal matrix. Acrawax facilitates the formation of continuous dense cell walls which is difficult to obtain using ordinary space holder materials. Moreover, acrawax is compressible in nature and it facilitates the formation of better and uniformly sized pores. Titanium foams have been synthesized utilizing acrawax in two different sizes. The effect of using differently sized acrawax on the cell walls and mechanical properties has also been carried out in this study.

Influence of quenching methods on martensitic transformation and mechanical properties of P/M processed Cu–Al–Ni–Ti shape memory alloys

The effect of quenching conditions on phase transformation characteristics and microstructural features of Cu–Al–Ni–Ti shape memory alloys (SMAs) have been studied. The alloys were synthesised via conventional powder metallurgy process using elemental metal powders. Four different quenching techniques, such as (a) two-step quenching, first to 100°C and then to 0°C; (b) two-step quenching, initially to 40°C and later to 0°C; (c) direct quenching to 40°C and (d) direct quenching to 0°C, were used. The microstructural features and phase transformations that the alloys had undergone were studied using FE-SEM and XRD techniques. The martensitic phase transformation analyses were carried out by differential scanning calorimeter while the mechanical properties were studied by microhardness and flexural bending tests. The results obtained clearly indicate that the quenching routes followed have a remarkable influence on the properties of Cu-based SMAs.