R.D. Cava

Atomization and Selective Laser Melting of a Cu-Al-Ni-Mn Shape Memory Alloy

Shape memory alloys (SMAs) are a class of material that undergoes a reversible shape change after a plastic deformation. The recovery of the original shape is possible due to a structural transformation upon heating to a critical temperature. The shape memory effect is related to a martensitic-austenitic transformation from a phase with a low symmetry (martensite) to a high-temperature phase (parent phase) [1]. Cu-based shape memory alloys have the advantage of large thermal and electrical conductivities and the system Cu-Al-Ni alloys are quite attractive due to better stabilisation against aging phenomena [2].

Phase Formation, Thermal Stability and Mechanical Properties of a Cu-Al-Ni-Mn Shape Memory Alloy Prepared by Selective Laser Melting

Selective laser melting (SLM) is an additive manufacturing process used to produce parts with complex geometries layer by layer. This rapid solidification method allows fabricating samples in a non-equilibrium state and with refined microstructure. In this work, this method is used to fabricate 3 mm diameter rods of a Cu-based shape memory alloy. The phase formation, thermal stability and mechanical properties were investigated and correlated. Samples with a relative density higher than 92% and without cracks were obtained. A single monoclinic martensitic phase was formed with average grain size ranging between 28 to 36 μm. The samples exhibit a reverse martensitic transformation temperature around 106 ± 2 °C and a large plasticity in compression (around 15±1%) with a typical “double-yielding” behaviour.

Microstructure of Spray Formed 2.9%C-22%Cr High Chromium White Cast Iron

In the present work a 2.9%C-22%Cr white cast iron was processed by spray forming aiming to investigate the potential of achieving novel microstructure by the high cooling rate involved in this process. Two gas flow rate to metal flow rate ratios (0.12 and 0.23) were used. The microstructural characterization was performed by using X-ray diffractometry, optical and scanning electron microscopy. The conventional microstructure of this alloy shows M 7 C 3 carbides (about 300 μm in length) embedded in a matrix of austenite and martensite dendrites; on the other hand the spray formed deposit showed a microstructure formed by fine M 7 C 3 carbides (less than 10 μm in length) in a martensitic matrix. The overspray powders showed a microstructure composed mainly by carbides and austenite; the relatively rapid solidification of the droplets enhanced the chromium and carbon solubility in austenite changing the Ms temperature.