Experimental Study On The Corrosion Resistance Of NiCr Alloy With TiN Coating

Objective: The purpose of this study was to investigate the corrosionresistance of NiCr alloy with titanium nitride(TiN) coating in artificial saliva.Methods:1NiCr alloy prepared:Forty-eight test specimens were fabricated throughthese steps: NiCr alloy casted, then required shape and size (3mm diameter,30mm high) cut by CNC machine, polished and smoothed by sandpaper.Then all the specimens were divided into A and B group randomly(each24).Each specimen in group A was treated by physical vapor deposition method,which created a2.5μm titanium nitride coating on the surface. Group B as acontrol without any treating. All the test specimens were warped up in epoxyresin, but left one end surface exposed, which the area was7.065mm~2. Afterwiped by95%alcohol, all specimens were immersed into artificial saliva for20minutes to make sure they were steady.2.Artificial saliva prepared: there were six different artificial saliva in thisexperiment: pH6.8(a), pH6.8with0.1%F-(b), pH6.8with0.2%F-(c), pH4(d),pH4with0.1%F-(e), pH4with0.2%F-(f).3.The free corrosion potential(Ecorr), Tafer diagram of curves andgalvanic current(Icorr) were tested and analysed by the classic three electrodessystem of electrochemical method in a,b,c,d,e,f artificial saliva differently.Results:1Free corrosion potential(Ecorr)1.1In b,c,d groups, E(A)>E(B,and showed significant differenc(ep<0.05);In a,e,f groups, E(A)>E(B), but had no significant difference(p<0.05).1.2Free corrosion potential(Ecorr) affected by different fluoride contentsin experimental and control group.Among pH6.8experiment groups, Ecorr showed significant differencebetween a,b,c.The result was E(a)>E(b)>E(c)(p<0.05). In PH4controlgroups, we got simiar result. In pH4, there was no significant difference for Ecorr between a,b,c inexperiment groups.The result was E(d)>E(e)>E(f)(p>0.05). but in control,p=0.052.1.3Free corrosion potential(Ecorr) affected by different PH inexperimental and control group.Ecorr showed no significant difference between E(a)>E(d)(p>0.05),Eb)>Ee()p>0.05), E(c)>E(f()p>0.05)in experiment groups,; while E(a)>E(d),(p=0.051), E(b)>E(e)(p>0.05), E(c)>E(f)(p<0.05)in control groups.2Galvanic current density (Icorr)2.1To find the differences of the galvanic current density between NiCralloy of titanium nitride(TiN) coating and NiCr alloy of untreated in a,b,c,d,e,fartificial saliva. In the a,c,d,e,f artificial saliva, I(A)was smaller than I(B)and hadsignificant difference (p<0.05). In the b artificial saliva, I(A)was smaller thanI(B)but had no significant difference (p>0.05).2.2Icorr affected by different fluoride contents in experimental andcontrol group.Among pH6.8experiment and control groups, Icorr showed significantdifference between a,b,c.The result was I(a)<I(b)<I(c)(,.p<0.05). In PH4controlgroups, we got same result.2.3Icorr affected by different PH in experimental and control group.Icorr showed: I(a)<I(d)(p>0.05), I(b)<I(e)(p>0.05), I(c)<I(f)(p<0.05)in experiment groups,; while I(a)<I(d),(p>0.05), I(b)>I(e)(p<0.05), I(c)>I(f)(p<0.05)in control groups.Conclusion:1In pH6.8and no fluoride artificial saliva, Free corrosion potential inNiCr alloy coating with titanium nitride(TiN) and in control did not showsignificant difference. The galvanic current density of NiCr alloy ofexperiment specimens were lower than that in control, what means TiN toNiCr has better quality of orrosion resistance of NiCr alloy. The change ofthe free corrosion potential and galvanic current density of NiCr alloy oftitanium nitride(TiN) coating was better than NiCr alloy of untreated of the corrosion resistance along with pH reduction and fluoride increasing.2In pH6.8artificial saliva enviroment, the free corrosion potential andgalvanic current density in experiment and control groups were both affectedwhen the fluoride increasing in artificial saliva. In the pH6.8artificial saliva,the free corrosion potential and galvanic current density of group A were notaffected when the fluoride increasing. NiCr alloy of untreated was affected alot of when the fluoride increasing.3In fluoride artificial saliva, the free corrosion potential of NiCr alloy oftitanium nitride was a little affected when the pH was decreasing, but the freecorrosion potential of group B was decreasing. The galvanic current density ofgroup A was affected smaller than group B.