Comparative Study on CuZnAl and CuMnZnAlNiFe Shape Memdory Alloys Subjected to Cavitation–Erosion

Abstract

After initial observations indicated that IIT using the Berkovich indenter was unable to produce any cracks in the laser-modified region, a cube corner indenter was used. Indentation was carried out for 5 different loads (400 mN, 200 mN, 100 mN, 50 mN, and 20 mN) in load-control mode, intended to determine the threshold load for cracking and resistance to fracture. Since a cube corner indenter is of much sharper geometry, the threshold load for cracking is much less and can be used for determining resistance to fracture of materials with toughness outside the regime of Berkovich or Vickers diamond [10,11]. Results were analyzed for maximum load-displacement during unloading.Both Berkovich and cube corner indentation impressions were analyzed by optical and scanning electron microscopy to determine cracking and/or separation of microstructural constituents and other features such as pile-up, sinkin, etc.The behavior of Cu-based shape memory alloys (SMA) subjected to cavitation±erosion has been studied at 22 and 5 C. CuZnAl alloys and Mn bronzes (CuMnZnAlNiFe) were tested by ultrasonic cavitation. The exposed samples were characterized through weight loss measures, scanning electron microscopy (SEM) and light microscopy (LM). The results of the tests at 22 C showed a higher resistance of CuZnAl alloys, particularly for the austenitic alloy (martensite start temperature (Ms) = -25 C), with a high reversibility of the martensitic transformation. In pseudoelastic Mn bronzes early martensite stabilisation was observed during the test, which is mainly attributed to the presence of precipitates. At 5 C the CuZnAl austenitic alloy showed a severe damage by intergranular cracking, while the rest of the alloys showed similar damage mechanisms.The term ªcavitationº derives from the latin word ªcavusº (hole), which means ªvoid formationº in fluid media. The formation of bubbles occurs as a result of the pressure reduction in a fluid below a critical value. As soon as the formed bubbles reach a condition of higher pressure, their implosion takes place. If the collapse of such bubbles occurs close to a solid surface, the material surface will be subjected to the local dissipation of a large energy amount. By the repeated occurrence of this process depending on the nature of the material, damage on the surface will eventually take place producing plastic deformation and volume loss. This removal of material caused by cavitation is called cavitation±erosion. The damage caused by cavitation±erosion can be observed in a large number of hydraulic components such as valves, propellers, hydraulic pumps, diesel engines, etc. SMA, principally from NiTi group, have showed high resistance to wear as well as to cavitation±erosion with exceptional long incubation periods (elapsed cavitation time without measurable weight loss). [1±6] This phenomenon has been understood by the capacity of these materials to absorb energy by a shape memory effect during bubble collapses. For

Laser Powder Bed Fusion of Cu–Al–Ni–Mn Shape‐Memory Alloy for the Application of Active Heat Sinks: Processability, Microstructures, and Shape‐Memory Effect

“…Additionally, the composition of the weld seam did not exhibit significant changes when compared to the base material. In recent years, three main families of Cu‐based SMAs, namely, Cu–Al–Ni, [ 7 ] Cu–Zn–Al, [ 8 ] and Cu–Al–Mn, [ 9 ] have been studied. Among them, the Cu–Al–Ni alloy is the most promising due to their improved thermodynamic stability, better ageing behavior, and wider transformation temperature.…”

Evaluation of cavitation-induced pressure loads applied to material surfaces by finite-element-assisted pit analysis and numerical investigation of the elasto-plastic deformation of metallic materials

“…Cavitation erosion is attributed to the collapse of individual cavitation bubbles in the vicinity of the material's surface [2]. Repeated collapses apply local cyclic pressure loads to the surface, which lead to damage and loss of material [3]. Quantitative knowledge of the induced pressure loads is crucial for understanding the material behavior and the underlying deformation processes.…”