電(dian)(dian)火(huo)(huo)花表(biao)(biao)面強(qiang)化(hua)是利用(yong)工(gong)具電(dian)(dian)極與(yu)工(gong)件(jian)間在氣體(ti)中產生的(de)(de)火(huo)(huo)花放電(dian)(dian)作用(yong)，把作為電(dian)(dian)極的(de)(de)導電(dian)(dian)材料(liao)熔滲進工(gong)件(jian)表(biao)(biao)層，形成合金(jin)化(hua)的(de)(de)表(biao)(biao)面強(qiang)化(hua)層，改(gai)善工(gong)件(jian)表(biao)(biao)面的(de)(de)物理及化(hua)學性(xing)能。
電火花表面強化層的性能主要決定于模具本身和電極材料，通常所用的電極材料有TiC、WC、ZrC、NbC、Cr3C2、硬質合金等。電火花強化表面因電極材料的沉積發生有規律的、較小的長大，除此之外，模具沒有其他變形。其心部的組織與性能也不發生變化，因此十分適用于工件表面強化處理。
金屬電(dian)(dian)(dian)火(huo)花(hua)表面(mian)強(qiang)化的(de)原理(li)是(shi)在工(gong)具電(dian)(dian)(dian)極(ji)與工(gong)件之間(jian)(jian)接上直(zhi)流電(dian)(dian)(dian)源或(huo)交流電(dian)(dian)(dian)源，由于振(zhen)動器的(de)作(zuo)用(yong)使電(dian)(dian)(dian)極(ji)與工(gong)件間(jian)(jian)的(de)放電(dian)(dian)(dian)間(jian)(jian)隙(xi)頻繁變化，工(gong)具電(dian)(dian)(dian)極(ji)與工(gong)件間(jian)(jian)不斷產生火(huo)花(hua)放電(dian)(dian)(dian)，從而實現(xian)對金屬表面(mian)的(de)強(qiang)化。
電(dian)(dian)(dian)(dian)(dian)(dian)(dian)火花(hua)強(qiang)(qiang)化(hua)過(guo)程如圖(tu)(tu)3-20所(suo)示。當(dang)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)極(ji)(ji)(ji)與(yu)工(gong)件(jian)(jian)(jian)(jian)之(zhi)間的(de)(de)(de)距離較(jiao)大時(shi)，電(dian)(dian)(dian)(dian)(dian)(dian)(dian)源經電(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻R對電(dian)(dian)(dian)(dian)(dian)(dian)(dian)容充電(dian)(dian)(dian)(dian)(dian)(dian)(dian)，電(dian)(dian)(dian)(dian)(dian)(dian)(dian)極(ji)(ji)(ji)在振(zhen)動(dong)器的(de)(de)(de)帶動(dong)下向模(mo)具靠近(jin)（見圖(tu)(tu)3-20a）。當(dang)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)極(ji)(ji)(ji)與(yu)模(mo)具之(zhi)間的(de)(de)(de)間隙接(jie)近(jin)到某(mou)個距離時(shi)，間隙中的(de)(de)(de)空氣在強(qiang)(qiang)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)場的(de)(de)(de)作用下電(dian)(dian)(dian)(dian)(dian)(dian)(dian)離，產(chan)生火花(hua)放(fang)(fang)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)（見圖(tu)(tu)3-20b），使電(dian)(dian)(dian)(dian)(dian)(dian)(dian)極(ji)(ji)(ji)和工(gong)件(jian)(jian)(jian)(jian)在發生放(fang)(fang)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)部分的(de)(de)(de)金屬局部熔化(hua)，甚至汽化(hua)。電(dian)(dian)(dian)(dian)(dian)(dian)(dian)極(ji)(ji)(ji)繼(ji)(ji)續(xu)接(jie)近(jin)工(gong)件(jian)(jian)(jian)(jian)并與(yu)工(gong)件(jian)(jian)(jian)(jian)接(jie)觸時(shi)，火花(hua)放(fang)(fang)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)停(ting)止，在接(jie)觸點流(liu)過(guo)短(duan)路(lu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)，使該處繼(ji)(ji)續(xu)加(jia)熱(re)，由(you)于電(dian)(dian)(dian)(dian)(dian)(dian)(dian)極(ji)(ji)(ji)以適(shi)當(dang)壓力壓向工(gong)件(jian)(jian)(jian)(jian)，使熔化(hua)的(de)(de)(de)材料互相粘接(jie)、擴散而形成合(he)金或新的(de)(de)(de)化(hua)合(he)物(wu)（見圖(tu)(tu)3-20c）。電(dian)(dian)(dian)(dian)(dian)(dian)(dian)極(ji)(ji)(ji)在振(zhen)動(dong)器的(de)(de)(de)作用下，離開(kai)了工(gong)件(jian)(jian)(jian)(jian)，放(fang)(fang)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)部分急劇冷卻（見圖(tu)(tu)3-20d）。經多(duo)次(ci)放(fang)(fang)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)，并相應地移動(dong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)極(ji)(ji)(ji)的(de)(de)(de)位(wei)置，則在零件(jian)(jian)(jian)(jian)表(biao)面形成強(qiang)(qiang)化(hua)層(ceng)。
電火(huo)(huo)花表面強化過程中發生了物(wu)理(li)化學(xue)變化，主(zhu)要包括超(chao)高(gao)速淬火(huo)(huo)、滲碳、滲氮、電極材(cai)料的轉移(yi)等。
a. 超高速淬火
電(dian)火花放(fang)電(dian)在(zai)模具表面的(de)極小面積上產生高溫，使(shi)該處的(de)金屬(shu)熔化和(he)部分(fen)汽化，當火花放(fang)電(dian)在(zai)極短(duan)的(de)時間內停止后，被加熱了的(de)金屬(shu)會以很快的(de)速度冷卻下來。這相(xiang)當于對模具表面層(ceng)進行了超速淬火。
b. 滲(shen)氮
在(zai)電火花放電通道區(qu)域內，溫度很高(gao)(gao)，空氣中的氮(dan)分(fen)子(zi)呈原子(zi)狀態，它和(he)受高(gao)(gao)溫而熔(rong)化的金(jin)屬有關的元素合成(cheng)高(gao)(gao)硬度的金(jin)屬氮(dan)化物，如氮(dan)化鐵、氮(dan)化鉻等。
c. 滲碳
來自石墨電(dian)極或周圍介質的(de)碳(tan)(tan)元素，熔解在受熱而熔化的(de)鐵中，形成金屬的(de)碳(tan)(tan)化物，如碳(tan)(tan)化鐵、碳(tan)(tan)化鉻等。
d. 電極材料的轉(zhuan)移
在操作壓力和火花放電的條(tiao)件下，電極材料轉(zhuan)移到模(mo)具金屬熔融表(biao)面，有關金屬合金元素（W、Ti、Cr等）迅速(su)擴散在金屬的表(biao)面層。
電火花表面強化層(ceng)具有如下特征：
a. 當(dang)采(cai)用硬質合金(jin)作電(dian)極(ji)材(cai)料時，硬度可(ke)達1100～1400HV（約(yue)70HRC以上）或更高，耐熱(re)性(xing)、耐蝕性(xing)和疲(pi)勞(lao)強(qiang)度都大大提高。
b. 當使用鉻(ge)錳、鎢鉻(ge)鈷合(he)金、硬質合(he)金作工(gong)具電(dian)極強化(hua)45鋼時，其耐磨性比原(yuan)表層提高2～2.5倍。
c. 用石墨(mo)作電極材料強化45鋼(gang)，用食鹽水(shui)作腐蝕性試驗，其(qi)耐蝕性提高90％；用WC、CrMn作電極強化不(bu)銹鋼(gang)時(shi)，其(qi)耐蝕性提高3～5倍。
d. 硬化層(ceng)厚(hou)度為0.01～0.08mm。
鋼制模(mo)具工(gong)作表(biao)面(mian)(mian)的電(dian)火花(hua)強化(hua)通常(chang)采用硬質合金電(dian)極(ji)。為了使(shi)被強化(hua)的表(biao)面(mian)(mian)光潔，事先必須將(jiang)模(mo)具和電(dian)極(ji)表(biao)面(mian)(mian)清洗(xi)干凈，然后手持(chi)(chi)振動器(qi)，將(jiang)電(dian)極(ji)沿模(mo)具工(gong)作表(biao)面(mian)(mian)移動，并保(bao)持(chi)(chi)適當(dang)壓力，使(shi)火花(hua)放(fang)電(dian)均勻連續(xu)。
電火花熔滲(shen)合金化層(ceng)的(de)形成是一(yi)個漸近過程(cheng)，在(zai)每一(yi)電規范下，合金化層(ceng)厚度出(chu)現最(zui)大(da)值，在(zai)通常使用(yong)的(de)電容范圍內，最(zui)佳單位(wei)面積涂覆時間為6～12min／c㎡。過分(fen)延(yan)長涂覆時間將出(chu)現層(ceng)厚減薄(bo)的(de)趨勢，并使性能惡化。可用(yong)直(zhi)線方程(cheng)式表示：
如電(dian)極YG8、電(dian)壓(ya)60V，頻率250Hz，電(dian)容60μF，最佳(jia)涂覆時間(jian)為6.75min／c㎡，合金化(hua)層厚(hou)度(du)為13μm；電(dian)容322μF，涂覆時間(jian)為11.99min／c㎡，合金化(hua)層厚(hou)度(du)為27μm。
為了降低合(he)(he)金(jin)(jin)化層的(de)(de)熱疲勞(lao)應(ying)力和電(dian)火(huo)(huo)花合(he)(he)金(jin)(jin)化處(chu)理(li)的(de)(de)應(ying)力，可(ke)穿插1～2次500℃×4h去應(ying)力退(tui)火(huo)(huo)，這(zhe)樣可(ke)獲(huo)得(de)性能優良、層深較厚的(de)(de)表面(mian)合(he)(he)金(jin)(jin)化層。改換電(dian)極(ji)材(cai)料，可(ke)使(shi)合(he)(he)金(jin)(jin)化層繼續增(zeng)厚，電(dian)極(ji)斷(duan)面(mian)尺寸(cun)不影響合(he)(he)金(jin)(jin)化層的(de)(de)厚度。鋼(gang)中(zhong)w（C）小于0.8％時(shi)(shi)，隨(sui)鋼(gang)中(zhong)碳(tan)含(han)量(liang)(liang)的(de)(de)增(zeng)加合(he)(he)金(jin)(jin)層增(zeng)厚；w（C）大于0.8％時(shi)(shi)，隨(sui)鋼(gang)中(zhong)碳(tan)含(han)量(liang)(liang)的(de)(de)增(zeng)加合(he)(he)金(jin)(jin)層變(bian)薄。
用YG8、Nb、Ti、Ta合金化(hua)，工(gong)件表面將獲得極高的顯(xian)微硬度值。
電火花合(he)(he)金(jin)(jin)層比(bi)未經電火花合(he)(he)金(jin)(jin)化處理(li)的模具的熱疲勞性能提高3倍，抗氧(yang)化性能提高兩倍，在各種試驗介質中(zhong)的耐(nai)蝕性提高3～15倍；表(biao)3-44所示(shi)為3Cr2W8V鋼的處理(li)效果(guo)。
電(dian)火花表(biao)面強化(hua)(hua)應用效果顯著(zhu)。例如用YG8作電(dian)極，對3Cr2W8V鋼模(mo)(mo)具進行電(dian)火花強化(hua)(hua)處理(li)以后(hou)，模(mo)(mo)具在(zai)各(ge)類酸堿中的(de)耐蝕性提高(gao)(gao)4～15倍；而(er)Cr12鋼模(mo)(mo)具刃口部位經電(dian)火花表(biao)面強化(hua)(hua)后(hou)，模(mo)(mo)具的(de)平均(jun)使用壽命由5萬次(ci)提高(gao)(gao)到20萬次(ci)。
