Experimental study demonstrates enhanced fracture toughness in CoNiAlSi ferromagnetic shape memory alloys modified with copper and phosphorus, indicating improved damage tolerance.
Key Points
To evaluate how copper and copper-phosphorus microalloying alters the microstructure, martensitic phase transformation, and local fracture toughness of CoNiAlSi ferromagnetic shape memory alloys.
Synthesized base CoNiAlSi, Cu-modified, and CuP-modified alloy ingots via vacuum induction melting under identical heat treatment conditions.
Characterized microstructure, phase evolution, and thermal transformation behavior using SEM, EDS, XRD, and DSC.
Assessed local mechanical response, plasticity, and fracture toughness using scratch testing and an energy-based nanoindentation load–displacement analysis.
Calculated fracture toughness rose from 10.53 MPa√m in the base CoNiAlSi alloy to 14.99 MPa√m with Cu addition (a 42% increase) and 21.08 MPa√m with CuP addition (a 100% increase).
Alloying additions preserved the thermally induced martensitic transformation and improved microstructural homogeneity without triggering new brittle phases.
Scratch tests revealed that while the base alloy possessed higher surface rigidity, Cu and CuP additions substantially enhanced plastic deformation capability.