Study of the Mechanical Properties and Microstructure of Spiral Tubes and Actuators for Controlled Extension Fabricated with Beryllium Bronze Strips

Abstract

QBe2.0 strips were used to fabricate spiral tubes and actuators for controlled extension (STACERs) through the winding and stabilization method, which is a novel technique for obtaining STACERs. The raw strips and the STACERs were investigated using tensile tests and SEM for the mechanical properties and fractography observation, employing specialized test equipment for service performance, and via XRD, EBSD, and TEM were used to test the residual stress and microstructure evolution. The tensile strength/elongation for raw strips was 485.8 MPa/60%, while for STACERs, tensile strength increased by 834.67 MPa to 646 MPa, and the elongation rate decreased by 12% to 19.3%. The fractography showed that the fracture mode was ductile. The service performance tests indicated that STACERs obtained under 320 °C had a higher driving force, good pointing accuracy, and high bending stiffness, while the residual stress of raw strips was τxy = −6 MPa; for STACERs obtained between 290 °C and 350 °C, τxy decreased from −5 MPa to −74 MPa, then increased from −74 MPa to 21 MPa, and the optimum fabricating parameter was 320 °C + 2 h. The EBSD results showed that LABs and HABs for raw strips and STACERs at 320 °C + 2 h accounted for 3–97% and 24.5–75.5%, the grain sizes were 7.07 μm and 3.67 μm, and the twin fraction decreased from 57.3% to 31.8%, respectively. The KAM and Schmid factor maps indicated that the STACER was prone to recovering and recrystallizing. Coupled with the EBSD results, the TEM results indicated that the strengthening mechanism for raw strips is twinning strengthening, while that for STACER is grain-refining strengthening with a precipitation of the γ″ phase. It is a meaningful novelty that the relationship between the macro properties and microstructure has been elucidated.

Special Issue: “Advanced Light Metal and Alloys: Preparation, Characterization, and Applications”

“…Shi et al [12] investigate the short-circuiting transfer, formation, and microstructure of Ti-6Al-4V alloy by external longitudinal magnetic field hybrid metal inert gas welding additive manufacturing. Cao et al [13] analyze microstructure evolution of the Ti-46Al-8Nb-2.5V alloy during hot compression and subsequent annealing at 900 • C. Lu et al [14,15] investigate the mechanical properties and microstructure of spiral tubes and actuators for controlled extension and retraction (STACERs) fabricated with beryllium bronze strips and Co40NiCrMo alloy. Porcaro et al [16] describe the results obtained from an archaeometric study of a bronze Nuragic small boat model (Sardinia, Italy) dating from the Early Iron Age (presumably 9th-7th centuries BC), which may help us understand the metallurgy and manufacturing process the Final Bronze and Early Iron Ages.…”