金剛石刀具的材料分為三種:天然單晶金剛石刀具(也就是咱們常說的鉆石)、人造聚晶金剛石(shi)、金剛石(shi)燒結體。由(you)于天然金剛石(shi)過于昂貴,所以市面上我們常用的都是人造聚晶金剛石(shi)刀(dao)具。
一、單晶金剛石用作超精密加工的優勢
1、有較高的(de)硬(ying)度和耐磨性,在超精(jing)密加工時可以最(zui)大限度避免(mian)刀尖磨損對工件尺寸的(de)影(ying)響。
2、有(you)很(hen)好的導熱(re)性,較低的熱(re)膨脹系(xi)數。因此,切削(xue)加工(gong)時不會產生很(hen)大的熱(re)變形,有(you)利于精(jing)密(mi)加工(gong)。
3、刃(ren)面(mian)粗(cu)糙(cao)度較小,刃(ren)口非常鋒利,可達Ra0.01~0.006μm。因此,能(neng)勝任(ren)薄層切削,有(you)利于超精密加工。
4、摩擦系數低(di),切削時(shi)不宜產生積屑瘤,因此加工表面(mian)質量很高(gao)。加工有色(se)金屬表面(mian)粗糙(cao)度(du)可小達Ra0.04~0.012μm,加工精度可(ke)達IT5以上。
注意:金(jin)(jin)剛(gang)石刀具不適合加(jia)工鋼鐵材料,因為金(jin)(jin)剛(gang)石和鐵有很強的化學親和力(li),在高溫下鐵原子極易與(yu)碳原子作(zuo)用(yong)而(er)使(shi)其轉化為石墨結構(gou),刀具極易損壞。用(yong)作(zuo)鋁硅合金(jin)(jin)的精(jing)(jing)(jing)加(jia)工及超(chao)精(jing)(jing)(jing)加(jia)工,壓縮木材、陶瓷、剛(gang)玉、玻璃等的精(jing)(jing)(jing)加(jia)工都(dou)是不錯(cuo)的選(xuan)擇。
二、單晶金剛石刀具的刃磨特點
超精密加(jia)工(gong)中,單晶(jing)金剛石刀(dao)(dao)(dao)具(ju)的(de)兩個基本精度是刀(dao)(dao)(dao)刃(ren)(ren)(ren)(ren)輪(lun)廓精度和刃(ren)(ren)(ren)(ren)口的(de)鈍(dun)圓半(ban)徑。要(yao)求加(jia)工(gong)非(fei)球面(mian)透鏡(jing)用(yong)的(de)圓弧刀(dao)(dao)(dao)具(ju)刃(ren)(ren)(ren)(ren)口的(de)圓度為(wei)0.05μm以下,加(jia)工(gong)多面(mian)體(ti)反射(she)鏡(jing)用(yong)的(de)刀(dao)(dao)(dao)刃(ren)(ren)(ren)(ren)直線度為(wei)0.02μm;刀(dao)(dao)(dao)具(ju)刃(ren)(ren)(ren)(ren)口的(de)鈍(dun)圓半(ban)徑(ρ值)表示(shi)了刀(dao)(dao)(dao)具(ju)刃(ren)(ren)(ren)(ren)口的(de)鋒利程度,為(wei)了適應各(ge)種(zhong)加(jia)工(gong)要(yao)求,刀(dao)(dao)(dao)刃(ren)(ren)(ren)(ren)刃(ren)(ren)(ren)(ren)口半(ban)徑范圍從20nm~1μm。
三、單晶金剛石刀具的晶面選擇
金(jin)(jin)剛(gang)石晶(jing)(jing)(jing)(jing)(jing)(jing)體(ti)屬于(yu)(yu)平面(mian)(mian)(mian)立(li)方晶(jing)(jing)(jing)(jing)(jing)(jing)系,由(you)于(yu)(yu)每個晶(jing)(jing)(jing)(jing)(jing)(jing)面(mian)(mian)(mian)上(shang)原子排列(lie)形式和(he)(he)原子密(mi)度(du)的(de)不(bu)同(tong)(tong)以及晶(jing)(jing)(jing)(jing)(jing)(jing)面(mian)(mian)(mian)之間(jian)距離的(de)不(bu)同(tong)(tong),造(zao)(zao)成天(tian)然金(jin)(jin)剛(gang)石晶(jing)(jing)(jing)(jing)(jing)(jing)體(ti)的(de)各(ge)向異性,因此金(jin)(jin)剛(gang)石不(bu)僅(jin)各(ge)晶(jing)(jing)(jing)(jing)(jing)(jing)面(mian)(mian)(mian)表(biao)現的(de)物理機械(xie)性能不(bu)同(tong)(tong)、其制(zhi)造(zao)(zao)難易程度(du)和(he)(he)使(shi)用(yong)(yong)壽命都不(bu)相同(tong)(tong),各(ge)晶(jing)(jing)(jing)(jing)(jing)(jing)面(mian)(mian)(mian)的(de)微(wei)(wei)觀(guan)破(po)損強度(du)也有(you)明顯差別。金(jin)(jin)剛(gang)石晶(jing)(jing)(jing)(jing)(jing)(jing)體(ti)的(de)微(wei)(wei)觀(guan)強度(du)可用(yong)(yong)Hertz試驗(yan)法來(lai)(lai)測定,由(you)于(yu)(yu)金(jin)(jin)剛(gang)石是典型的(de)脆(cui)性材料,其強度(du)數(shu)值一般偏差較(jiao)(jiao)大(da),主(zhu)要(yao)依賴于(yu)(yu)應力(li)分布的(de)形態和(he)(he)分布范圍,因此適合(he)用(yong)(yong)概率(lv)論(lun)來(lai)(lai)分析。當作(zuo)用(yong)(yong)應力(li)相同(tong)(tong)時,(110)晶(jing)(jing)(jing)(jing)(jing)(jing)面(mian)(mian)(mian)的(de)破(po)損概率(lv)最大(da),(111)晶(jing)(jing)(jing)(jing)(jing)(jing)面(mian)(mian)(mian)次之,(100)晶(jing)(jing)(jing)(jing)(jing)(jing)面(mian)(mian)(mian)產生破(po)損的(de)概率(lv)最小。即(ji)在(zai)外力(li)作(zuo)用(yong)(yong)下,(110)晶(jing)(jing)(jing)(jing)(jing)(jing)面(mian)(mian)(mian)最易破(po)損,(111)晶(jing)(jing)(jing)(jing)(jing)(jing)面(mian)(mian)(mian)次之,(100)最不(bu)易破(po)損。盡管(110)晶(jing)(jing)(jing)(jing)(jing)(jing)面(mian)(mian)(mian)的(de)磨(mo)削率(lv)高(gao)于(yu)(yu)(100)晶(jing)(jing)(jing)(jing)(jing)(jing)面(mian)(mian)(mian),但實驗(yan)結果表(biao)明,(100)晶(jing)(jing)(jing)(jing)(jing)(jing)面(mian)(mian)(mian)較(jiao)(jiao)其它(ta)晶(jing)(jing)(jing)(jing)(jing)(jing)面(mian)(mian)(mian)具(ju)有(you)更(geng)高(gao)的(de)抗應力(li)、腐蝕和(he)(he)熱(re)退(tui)化能力(li)。結合(he)微(wei)(wei)觀(guan)強度(du)綜合(he)考慮,用(yong)(yong)(100)面(mian)(mian)(mian)做(zuo)刀(dao)具(ju)的(de)前后刀(dao)面(mian)(mian)(mian),容(rong)易刃磨(mo)出(chu)高(gao)質量的(de)刀(dao)具(ju)刃口,不(bu)易產生微(wei)(wei)觀(guan)崩(beng)刃。
通常應根據刀(dao)(dao)(dao)(dao)具(ju)(ju)(ju)的(de)(de)(de)要(yao)(yao)(yao)求(qiu)來進行單晶(jing)(jing)金(jin)剛石刀(dao)(dao)(dao)(dao)具(ju)(ju)(ju)的(de)(de)(de)晶(jing)(jing)面(mian)選擇。一般來說,如(ru)(ru)果要(yao)(yao)(yao)求(qiu)金(jin)剛石刀(dao)(dao)(dao)(dao)具(ju)(ju)(ju)獲得最高的(de)(de)(de)強度,應選用(yong)(100)晶(jing)(jing)面(mian)作(zuo)(zuo)(zuo)為刀(dao)(dao)(dao)(dao)具(ju)(ju)(ju)的(de)(de)(de)前(qian)(qian)、后(hou)(hou)刀(dao)(dao)(dao)(dao)面(mian);如(ru)(ru)果要(yao)(yao)(yao)求(qiu)金(jin)剛石刀(dao)(dao)(dao)(dao)具(ju)(ju)(ju)抗(kang)(kang)機械磨損,則(ze)選用(yong)(110)晶(jing)(jing)面(mian)作(zuo)(zuo)(zuo)為刀(dao)(dao)(dao)(dao)具(ju)(ju)(ju)的(de)(de)(de)前(qian)(qian)、后(hou)(hou)刀(dao)(dao)(dao)(dao)面(mian);如(ru)(ru)果要(yao)(yao)(yao)求(qiu)金(jin)剛石刀(dao)(dao)(dao)(dao)具(ju)(ju)(ju)抗(kang)(kang)化(hua)學(xue)磨損,則(ze)宜采(cai)用(yong)(110)晶(jing)(jing)面(mian)作(zuo)(zuo)(zuo)刀(dao)(dao)(dao)(dao)具(ju)(ju)(ju)的(de)(de)(de)前(qian)(qian)刀(dao)(dao)(dao)(dao)面(mian),(100)晶(jing)(jing)面(mian)作(zuo)(zuo)(zuo)后(hou)(hou)刀(dao)(dao)(dao)(dao)面(mian),或者前(qian)(qian)、后(hou)(hou)刀(dao)(dao)(dao)(dao)面(mian)都(dou)采(cai)用(yong)(100)晶(jing)(jing)面(mian)。這些要(yao)(yao)(yao)求(qiu)都(dou)需要(yao)(yao)(yao)借助晶(jing)(jing)體定(ding)向技術(shu)來實現。
四、單晶金剛石的物理特性
金剛石是(shi)單一碳(tan)(tan)原(yuan)子的結(jie)晶(jing)體(ti)(ti),其晶(jing)體(ti)(ti)結(jie)構屬(shu)于等軸面心立方晶(jing)系(一種(zhong)原(yuan)子密度最(zui)高的晶(jing)系)。由(you)于金(jin)剛(gang)石中(zhong)碳(tan)(tan)原(yuan)子間的連接鍵為sp3雜化共價鍵,因此具有很(hen)強(qiang)的結(jie)合力(li)、穩定性和方向(xiang)性。它是(shi)目前自然(ran)界(jie)已知的最(zui)硬(ying)(ying)物質,其顯微硬(ying)(ying)度可達10000HV,其它物理特性見以下內容。
物理性能-數值
硬度-60000~100000MPa,隨晶體方向(xiang)和溫度而定
抗彎強度-210~490MPa
抗壓強度-1500~2500MPa
彈性模量-(9~10.5)×10的12次(ci)方MPa
熱(re)導率(lv)-8.4~16.7J/cm·s·℃
質量熱容-0.156J/(g·℃)(常溫(wen))
開始氧化溫度-900~1000K
開始石墨化溫度-1800K(在惰(duo)性氣體(ti)中(zhong))
和鋁(lv)合(he)金、黃銅間的摩擦系數(shu)-0.05~0.07(在常溫下(xia))