Microstructural control and evaluation of a FCC Cr-Co-Ni multi-principal element alloy with carbon-doping

• Autor(a) principal: Guilherme Cardeal Stumpf
• Data de Publicação: 2023
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Repositório Institucional da UFMG
• Texto Completo: http://hdl.handle.net/1843/57570
• topic: Multi-principal element alloys; Cr-Co-Ni; Carbon-doping; Hall-Petch; Microstructure evolution; Severe plastic deformation; Engenharia metalúrgica; Metalurgia física; Carbono; Ligas; Plástico - Deformação

The multi-principal element alloys (MPEAs) field is characterized by a change in conception for the design of new materials. By exploring compositions with three or more elements in high concentrations, the limit of possibilities compared to conventional alloys is expanded. In recent years, Cr-Co-Ni fcc (face-centered cubic) alloys have drawn significant attention due to their high mechanical properties, corrosion resistance, and especially due to their toughness ranking amongst the highest of all known materials. This work aims to study the effects of carbon-doping to the microstructure and mechanical properties of the Cr40Co30Ni30 alloy. To analyze how this element, be it in solid solution and/or in precipitates, affect the grain size control and refinement, two compositions were designed and fabricated, Cr39.9Co30Ni30C0.1 and Cr39.1Co30Ni30C0.4, respectively. Both alloys, as well as the base material, were processed in three different routes to study carbon-doping after: solution treatment, coarse (and heterogeneous) precipitation and severe plastic deformation. The microstructure and Hall-Petch relation were investigated with the aid of different characterization techniques. Carbon-doping was observed to be more effective in retarding grain growth with a prior solution treatment, resulting in a homogeneous particle distribution achieved after processing. Additionally, its contribution to hardness was mainly due to grain size refinement, with virtually no observed increments from precipitation or interstitial strengthening. Under sever plastic deformation, carbon-doping deactivated twinning induced plasticity (TWIP) and phase transformation induced plasticity (TRIP), inducing a nanostructured network of stacking faults.