Abstract
The effect of heat treatment on tensile and low cycle fatigue properties of the oxygen-free copper for electric power equipment was investigated. The heat treatment at 850 °C for 20 min, which corresponds to the vacuum brazing process, caused the grain growth and relaxation of strain by recrystallization, and thus, the residual stress in the oxygen-free copper was reduced. The tensile strength and 0.2% proof stress were decreased, and elongation was increased by the heat treatment accompanying recrystallization. The plastic strain in the heat-treated specimen was increased compared with that in the untreated specimen under the same stress amplitude condition, and thus, the low cycle fatigue life of the oxygen-free copper was degraded by the heat treatment. Striation was observed in the crack initiation area of the fractured surface in the case of the stress amplitude less than 100 MPa regardless of the presence of the heat treatment. With an increase in the stress amplitude, the river pattern and the quasicleavage fracture were mainly observed in the fracture surfaces of the untreated specimens, and they were observed with striations in the fracture surfaces of the heat-treated ones. The result of the electron backscattered diffraction (EBSD) analysis showed that the grain reference orientation deviation (GROD) map was confirmed to be effective to investigate the fatigue damage degree in the grain by low cycle fatigue. In addition, the EBSD analysis revealed that the grains were deformed, and the GROD value reached approximately 28° in the fractured areas of heat-treated specimens after the low cycle fatigue test.
Highlights
The demand of capacity enlargement of power supply used for power generation and electric transportation facilities has been increasing due to the increase of the electricity demand, steady supply of the electric power system, and low environmental impact
An electron backscattering diffraction (EBSD) analysis was conducted to the surface of the specimen after Ar milling to investigate the fatigue damage behavior using an EBSD system (TSL MSC-2200, TexSEM Laboratories, Inc., Provo, UT, USA) equipped with the field emission scanning electron microscope (FE-SEM)
The result of the EBSD analysis showed that a noisy inverse pole figure (IPF) map was obtained in the untreated specimen
Summary
The demand of capacity enlargement of power supply used for power generation and electric transportation facilities has been increasing due to the increase of the electricity demand, steady supply of the electric power system, and low environmental impact. The mechanical stress loaded in the contact materials is increased due to the thermal expansion by heating. In such materials, it is important to investigate the fatigue properties in a low cycle fatigue area by high stress. Copper has been used for conductor parts of the electric power equipment due to its high conductivity [2,3]. The oxygen-free copper has many advantages s2uocf h14 as gas tolerance at an electric discharge, low discharge of hydrogen gas, and vacuum deterioration tolerance [4], and it has been used for the various types of electric power esquucihpmasegnat.s Gtoelnerearnalcley,athaignhecleycctlreicfadtiisgcuheartgeest,slohwavdeisbceheanrgceonofdhuyctderdoginenmgeatsa,lsa.nAdlvthaocuuugmh sdimetielarirotreasttiosnhatovleerbaenecne a[4ls],oacnodntdhuucst,eidt hinaspbuereencuospepdefroarnthdecvoaprpioeur saltlyopyess[o5f–e1l2e]c,ttrhicepreowareer aeqfeuwipmexepnetr.iGmeennetaral llrye,shuilgtsh ocfyctlheefaotxigyugeente-fsrtesehacovpepbeerenincothneduloctwedciynclme eftaatlisg.uAeltrheoguiognh [5si,m10i,l1a1r]t.eIsntsahdadviteiobne,enthaelsooxycognednu-fcrteeedcionpppuerrepcaorptspuerseadndincothpepeelreacltlroicysp[o5w–1e2r]e, qthueirpemaerenta ufnewdeerxgpoearihmeeantttarleraetsmueltnstopf rtohceeosxsysguecnh-farseebcroazpipnegr [i1n3t]h, eanlodwthcyucsl,ethfaetiignuveesretiggiaotnio[n5,1o0f,f1a1-]. Brazing with the Ag-Cu based filler metal is usually conducted on a vacuum condTihtiuosn, [t1h3e,1a4i]m, anodf tthhies bsrtauzdiyngiscytocleinivnetshtiegraetael tphreodefufcetctisorfelhaetiavteclyclloenigntitmhee b[1r6a]z.ing proceTsshouns, tthheelaoiwmcoyfcltehifsatsitguudeypirsotpoerintivesesotfigtahtee othxyegeefnfe-cfrteoefchoepaptecry. cFlueritnhetrhme obrrea,ztihneg eplercotcreosns boanctkhsecalottwerecdycdleiffaraticgtiuoenp(rEoBpSeDrt)ieasnoaflythsies owxaysgecno-nfdreuectceodpptoeri.nFvuersthigeartme othree, ftah-e tiegleucetrdoanmbagckesbceahttaevreiodrdoifftrhaecthioenat(-EtrBeSaDte)daonxaylygseisn-wfraeseccoonpdpuecrt.ed to investigate the fatigue damage behavior of the heat-treated oxygen-free copper
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