Comparison of the corrosion resistance and the mechanical stability after corrosion of 3D printing and cast cobalt-chromium alloy

Objective To compare the corrosion resistance and the mechanical stability after corrosion of 3D printing and cast cobalt-chromium (Co-Cr) alloy. Methods The Co-Cr alloys were fabricated by the selective laser melting (SLM) technique and casting technique with suitable parameters, seventy-two specimens were prepared and divided into 12 groups (n= 6) by random number method. Static immersion test was used to evaluate corrosion resistance and the effect of the corrosion on the mechanical stability of the alloys. Surface roughness (Ra) , vickers hardness (VHN) , tensile strength (TS) and bending strength (BS) of the samples were analyzed separately by confocal laser scanning microscope (CLSM) , vicker microhardness tester, universal testing machine. The results were analyzed by 2×2 factorial design analysis of variance (α= 0.05) , the pairwise comparison was performed with Bonferroni method. Results Manufacturing methods and corrosion had no interaction effects on Ra and BS (FRa= 2.989, PRa= 0.099; FBS= 0.480, PBS= 0.496) . The two factors′ main effects on Ra had significant differences (Fmethod= 6.262, Pmethod= 0.021; Fcorrosion= 6.581, Pcorrosion= 0.018) . The Ra of 3D group was lower than that of cast group [Ra3D= (0.084 ± 0.026) μm, Racast= (0.111 ± 0.024) μm]. The Ra of contrast group was lower than that of corrosion group[Racontrast= (0.084 ± 0.025) μm, Racorrosion= (0.111 ± 0.025) μm]. The two factors′ main effects on BS had significant differences (Fmethod= 6.753, Pmethod= 0.013; Fcorrosion= 7.384, Pcorrosion= 0.017) . The BS of 3D group was higher than that of cast group [BS3D= (1651 ± 242) MPa, BScast= (1371 ± 252) MPa]. The BS of contrast group was higher than that of corrosion group [BScontrast= (1645 ± 183) MPa, BScorrosion= (1377 ± 310) MPa]. Manufacturing methods and corrosion had interaction effects on VHN and TS (FVHN= 5.018, PVHN= 0.037; FTS= 5.903, PTS= 0.025) . The results of the pairwise comparison of Bonferroni method suggested significant differences on VHN and TS (PVHN<0.001, PTS<0.001) were found between the 3D contrast group [VHN3D= (469 ± 4) HV, TS3D= (1010 ± 46) MPa] and the cast contrast group [VHNcast= (418 ± 4) HV, TScast= (827 ± 25) MPa], significant differences on VHN and TS (PVHN<0.001, PTS<0.001) were observed between the 3D corrosion group [VHN3D= (418 ± 3) HV, TS3D= (985 ± 30) MPa] and the cast corrosion group [VHNcast= (375 ± 5) HV, TScast= (728 ± 45) MPa]. Significant differences on VHN (P<0.001) were found between the 3D contrast group and the 3D corrosion group. No significant differences on TS (P= 1.000) were found between the 3D contrast group and the 3D corrosion group. Significant differences on VHN and TS (PVHN<0.001, PTS<0.001) were observed between the cast contrast group and the cast corrosion group. Conclusions The 3D printing Co-Cr alloy has better corrosion resistance than that of the cast Co-Cr alloy. The 3D printing Co-Cr alloy has better stability of the TS and BS than that of the cast Co-Cr alloy. Both kinds of alloys have equal stability of VHN. Key words: 3D printing; Selective laser melting; Cobalt-chromium alloy; Corrosion resistance; Mechanical stability