Study On Microstructure And Arc Ablation Behavior Of Ultra-fine CuCr Alloy Prepared By Friction Stir Processing

CuCr alloy,lauded for its superior electrical and thermal conductivities,robust interruption ability,and remarkable resistance to high voltage and arc erosion,finds extensive applications in high-voltage switches.Nevertheless,conventional fabrication methodologies of CuCr alloys grapple with challenges like internal flaws and the uneven distribution of oversized Cr phases.Addressing these hurdles,this research pivots on the CuCr30 alloy,suggesting the utilization of Friction Stir Processing(FSP)for the optimization of CuCr30 alloy’s microstructure and performance,and contrasting it with counterparts manufactured via Selective Laser Melting(SLM).A comprehensive exploration is embarked on,encompassing the spheres of defect prognostication,microstructural evolution,arc erosion behavior,and underlying mechanisms.Based on the examination of diverse rotational speed impacts on the formability,the optimum processing parameters are earmarked for distinct FSP passes,shedding light primarily on the interplay between the evolution of the CuCr30 alloy’s microstructure following diverse FSP passes and annealing heat treatment and its influence on arc erosion performance.Adopting a synergistic approach of finite element numerical simulation and experimental validation,the temperature distribution and plastic deformation characteristics of CuCr30 alloy amidst FSP are thoroughly investigated.The study culminates in the identification of the optimal manufacturing parameters,namely a rotational speed of 1600 r/min and a processing speed of 10 mm/min,within a forming temperature window approximating 900℃to 1000℃.With the rotational speed escalating from 600 r/min to 1600 r/min,the peak processing temperature surges from459℃to 1030℃,and the plastic deformation transitions from a disorderly tumultuous flow to an orderly,stable current in the direction of the stirring pin’s rotation.Upon executing 1 and 8 passes of FSP on the CuCr30 alloy,both the Cu and Cr phases undergo refinement,catalyzed by the shearing disintegration induced by the stirring pin,with the Cu phase manifesting dynamic recrystallization.With the multiplication of FSP passes,the Cr phase grain size shrinks to 110 nm,and the dislocation density experiences a considerable surge.Post annealing heat treatment,static recrystallization unfolds in the Cu phase,leading to a decrease in grain size.The amalgamation of grain refinement,dislocation fortification,and solid-solution strengthening yields a substantial escalation in micro-hardness,reaching 477.7 HV,marking an amplification of 417%,concurrently maintaining electrical conductivity at over 95%of its initial level.Compared to the samples processed via Selective Laser Melting(SLM),the FSP procedure renders a notable enhancement in the alloy’s microstructure and properties.In vacuum breakdown trials,BM samples exhibit concentrated erosion traits,predominantly in the Cr phase.A single pass of FSP ameliorates Cr refinement,yet the erosion traits continue to be uneven.Following 8 passes of FSP,the refined and homogenized microstructure effectively diffuses the arc energy,resulting in erosion primarily in the high-energy grain boundaries and phase boundaries,thereby demonstrating uniform erosion traits.Post annealing,the 8-pass FSP specimens showcase markedly improved erosion resistance.In contrast to BM specimens,the mass loss post1,30,and 100 breakdowns diminishes by 50%,82.4%,and 59%respectively,attaining an electric field strength of 10.8×10~7 V/m after 30 breakdowns.Although heat treatment enhances the erosion resistance of SLM specimens,their erosion characteristics and overall performance remain inferior to those of the 8-pass FSP specimens.After one breakdown,30 breakdown and 100 breakdown,the mass loss of FSP 8heat treatment samples is 0.01 mg,0.16 mg and 11.1 mg respectively,which are reduced by 50%,82.4%and 59%compared with BM respectively.After 30 breakdown,the breakdown field strength reaches 10.8×107 V/m.For SLM samples,compared with the samples without heat treatment,the ablative properties of SLM samples are improved after heat treatment,but the ablative properties of SLM samples are improved after heat treatment,and the ablative properties of SLM samples are selectively occurred from Cr phase and unfused pores.