傳統(tǒng)合金由一種基本元素和少量元素組成 隨著現(xiàn)代工業(yè)的發(fā)展，新型的“多主元合金”(Multi-principal element alloys, MPEAs)應(yīng)運(yùn)而生[1~4] 多主元合金由三至四種元素按等原子比或近等原子比生成中熵合金(Medium entropy alloy, MEA)，五種及以上主要元素生成的合金稱為高熵合金(High entropy alloy, HEA)[5] 多主元合金具有高熵效應(yīng)、緩慢擴(kuò)散效應(yīng)、晶格畸變效應(yīng)和雞尾酒效應(yīng)[1, 2]，因此多主元合金在高溫、強(qiáng)輻照、高摩擦以及強(qiáng)腐蝕等極端領(lǐng)域有廣闊的應(yīng)用前景[6~13]

多主元合金中不同組元原子半徑的差異產(chǎn)生嚴(yán)重的晶格畸變，阻礙位錯(cuò)的運(yùn)動(dòng) 因此，晶格畸變是多主元合金固溶強(qiáng)化的關(guān)鍵因素[14~16] VCoNi中熵合金具有典型的晶格畸變效應(yīng)，其抗拉強(qiáng)度接近1 GPa，伸長(zhǎng)率約為55%，實(shí)現(xiàn)了優(yōu)異的強(qiáng)韌化性能協(xié)調(diào)[16, 17] 其原因是，V原子顯著增大了原子鍵距的波動(dòng)，嚴(yán)重的晶格畸變使位錯(cuò)移動(dòng)需要的晶格摩擦應(yīng)力顯著提高[16]

與傳統(tǒng)合金類(lèi)似，添加間隙原子可產(chǎn)生間隙強(qiáng)化和第二相強(qiáng)化[18, 19] 碳(C)是應(yīng)用最多的間隙原子之一 在CoCrNi中熵合金中加入C(0.75%，原子分?jǐn)?shù))，可使其強(qiáng)度提高且保持著75%左右的延伸率[20] 其原因是，C產(chǎn)生的間隙固溶強(qiáng)化提高了合金層錯(cuò)能，從而延緩孿晶的產(chǎn)生并減小孿晶層的厚度 這些細(xì)小的孿晶組織，可延緩塑性失穩(wěn)并顯著提高合金的加工硬化能力 在FeCoNiCrMn高熵合金中加入少量的C(0.1%，原子分?jǐn)?shù))，可使其在變形過(guò)程中產(chǎn)生更高密度的位錯(cuò)和后續(xù)退火中孿晶界的比例顯著降低，因?yàn)镃原子使合金的層錯(cuò)能增大[21] Fe49.5Mn30Co10Cr10C0.5高熵合金的低溫(77 K)抗拉強(qiáng)度(1300 MPa)[22]比室溫顯著提高，且具有出色的延伸率(50%) 其原因是，C原子產(chǎn)生的間隙固溶強(qiáng)化和合金層錯(cuò)能的降低提高了晶格摩擦力，使位錯(cuò)滑移方式由波浪滑移轉(zhuǎn)變?yōu)槠矫婊?

在合金的變形和熱處理過(guò)程中發(fā)生的織構(gòu)變化使樣品產(chǎn)生各向異性，因此研究其織構(gòu)演變至關(guān)重要 例如，冷軋?zhí)幚砗蟮腃oCrNi中熵合金產(chǎn)生以Brass為主的形變織構(gòu)，而熱軋樣品則產(chǎn)生明顯的α取向且Brass織構(gòu)強(qiáng)度降低；熱處理后CoCrNi合金中的再結(jié)晶晶粒仍保留大量的形變織構(gòu)組分，即以α取向?yàn)橹鞯脑俳Y(jié)晶織構(gòu)[23] Bhattacharjee等[24]研究了CoCrFeMnNi合金冷軋和退火后的織構(gòu)演變，發(fā)現(xiàn)冷軋90%后出現(xiàn)強(qiáng)Brass型織構(gòu)，而再結(jié)晶織構(gòu)中保留了Brass變形織構(gòu)組分，但是新形成的S織構(gòu)比Brass織構(gòu)更強(qiáng)

對(duì)于力學(xué)性能出色的多主元合金，其在摩擦服役條件下的服役性能受到極大的關(guān)注 C原子摻雜使CoCrFeMnNiC x 合金的摩擦磨損性能提高[25]，因?yàn)樯傻挠睲7C3碳化物(M主要為Cr、Fe和Mn)使磨損表面的分層行為減弱 用激光熔覆技術(shù)在45鋼表面制備的CoCrFeMnNiC x 改性層[26]，隨著C含量由0提高到0.09涂層的摩擦因數(shù)降低而耐磨性能提高 其原因是，析出的硬質(zhì)碳化物M23C6保護(hù)了磨損表面 在Fe50Mn30Co10Cr10基體中添加B4C陶瓷顆粒使其具有比基體更高的摩擦磨損能力[27]，因?yàn)锽4C顆粒在基體材料中產(chǎn)生彌散強(qiáng)化和細(xì)晶強(qiáng)化，使磨損率和摩擦系數(shù)顯著降低 鑒于此，本文在VCoNi中熵合金中添加不同含量的C原子制備(VCoNi)100-x C x (x=0，0.1，0.4，1和2.8)中熵合金，系統(tǒng)研究C含量對(duì)VCoNi中熵合金的微觀組織演變、力學(xué)性能以及摩擦磨損性能的影響

1 實(shí)驗(yàn)方法

實(shí)驗(yàn)用原料為高純粉末V、Co、Ni和C(其純度均高于99.9%) 以氬氣作為保護(hù)氣體，用真空非自耗電弧爐熔煉(VCoNi)100-x C x (x=0，0.1，0.4，1和2.8)樣品 根據(jù)添加C原子的比例，將樣品命名為CX 先將金屬粉末充分混合，然后壓成直徑為10 mm、高約為10 mm的圓柱體 將圓柱體放入真空非自耗電弧熔煉爐的水冷銅坩堝中進(jìn)行熔煉，為了保證樣品的均勻性，每個(gè)樣品至少翻轉(zhuǎn)重熔4次，得到鑄態(tài)樣品 隨后將鑄態(tài)樣品在1000℃保溫2 h后進(jìn)行熱壓縮變形(變形量45%)，再將熱壓態(tài)樣品在1000℃保溫2 h后水淬，得到均勻態(tài)樣品

用電火花線切割機(jī)將均勻態(tài)樣品切片，然后進(jìn)行室溫軋制變形(變形量70%)，并將其在1000℃保溫1 min后水淬，得到再結(jié)晶態(tài)樣品

使用配備有EDS分析儀和EBSD探頭的ZEISS SIGMA HD場(chǎng)發(fā)射掃描電鏡(SEM)觀察樣品的微觀組織及元素分布 先用砂紙將SEM樣品水磨至3000#，再進(jìn)行電解拋光 電解拋光液的成分為高氯酸和乙醇(體積比1∶9)，拋光溫度約為-30℃ 電解拋光時(shí)將樣品接直流穩(wěn)壓電源的陽(yáng)極，用不銹鋼作陰極，在電壓為20 V、電流為0.25 A條件下電化學(xué)拋光約50 s 用Channel 5后處理軟件分析EBSD數(shù)據(jù) 用萬(wàn)能拉伸實(shí)驗(yàn)機(jī)測(cè)試室溫拉伸性能，拉伸應(yīng)變速率為3 mm/min，試樣標(biāo)距長(zhǎng)度45 mm，寬10 mm和厚2 mm，其形狀似“狗骨狀” 使用圓盤(pán)式磨損試驗(yàn)機(jī)進(jìn)行室溫摩擦磨損實(shí)驗(yàn)，試樣的長(zhǎng)度為20 mm、寬為10 mm、厚為2 mm，使用直徑為6 mm的Al2O3球作為摩擦副，旋轉(zhuǎn)半徑為3 mm，轉(zhuǎn)動(dòng)速度為200 r/min，載荷為10 N，測(cè)試時(shí)長(zhǎng)為30 min 用Bruker白光干涉儀測(cè)量摩擦磨損樣品磨痕的三維形貌，使用Vision 64軟件處理干涉儀數(shù)據(jù)得到磨損三維形貌和磨損體積

使用Thermo-Calc軟件(Version 2020a)進(jìn)行CALPHAD計(jì)算并根據(jù)熱力學(xué)數(shù)據(jù)庫(kù)TCHEA 4[28]，繪制出(VCoNi)100-x C x (x=0，0.1，0.4，1和2.8)樣品的相含量隨溫度變化，以分析其主要相結(jié)構(gòu)

2 實(shí)驗(yàn)結(jié)果

圖1給出了(VCoNi)100-x C x (x=0，0.1，0.4，1和2.8)的相含量隨溫度變化 x=0時(shí)(圖1a)，高溫相區(qū)(870~1253℃)的結(jié)構(gòu)為單相FCC，在低溫相區(qū)(600~869℃)出現(xiàn)金屬間化合物Co3V、D022(Al3Ti型)和σ相 x=0.1時(shí)(圖1b)，合金的熔點(diǎn)略有降低(1212℃)，σ相的析出溫度升高(1120℃)，在1238℃開(kāi)始析出少量HCP相 x=0.4時(shí)(圖1c)，合金的熔點(diǎn)提高(1230℃)，σ相的析出溫度降低(940℃)，HCP相的析出溫度升高(1330℃)且其含量提高 x=1時(shí)(圖1d)，合金的熔點(diǎn)繼續(xù)提高(1270℃)，在溫度區(qū)間1460~1500℃析出FCC相，且隨著溫度的降低出現(xiàn)HCP相(1472℃)、σ相(787℃) x=2.8時(shí)(圖1e)，合金的熔點(diǎn)提高到1343℃，σ相消失，在1290℃析出M3C2型(M=V、Co)碳化物，F(xiàn)CC相區(qū)擴(kuò)寬(1269~1500℃)，HCP相區(qū)變窄(786~1080℃) 這表明，隨著含C含量的提高，金的熔點(diǎn)呈現(xiàn)升高的趨勢(shì)，HCP相的含量先提高后降低，σ相的含量逐漸降低

圖1



圖1(VCoNi)100-x C x (x=0，0.1，0.4，1和2.8)的相含量隨溫度的變化

Fig.1Phases fraction as function of temperature for (VCoNi)100-x C x (x=0, 0.1, 0.4, 1 and 2.8) samples (a) C0; (b) C0.1; (c) C0.4; (d) C1; (e) C2.8

圖2給出了均勻態(tài)(VCoNi)100-x C x (x=0，0.1，0.4，1和2.8)樣品的SEM形貌 C0(圖2a)、C0.1(圖2b)和C0.4樣品(圖2c)的晶粒均呈等軸晶形態(tài)，退火孿晶呈板條狀，平均晶粒尺寸分別為40 μm(圖2a)，32 μm(圖2b)和21 μm(圖2c) C1樣品(圖2d)的晶粒呈等軸晶和胞狀晶，平均晶粒尺寸為28 μm，在等軸晶中也觀察到退火孿晶 C2.8樣品(圖2e)的晶粒呈胞狀形態(tài)，沒(méi)有退火孿晶，平均晶粒尺寸為49 μm 同時(shí)，隨著C含量的提高，均能觀察到不同形態(tài)的第二相顆粒；C0.1、C0.4和C1樣品中的第二相以棒狀和顆粒狀形態(tài)為主；而C2.8樣品中的第二相則呈條狀、棒狀和顆粒狀

圖2



圖2均勻態(tài)(VCoNi)100-x C x (x=0，0.1，0.4，1和2.8)的SEM照片

Fig.2SEM images of as-homogenized samples: (a) C0; (b) C0.1; (c) C0.4; (d) C1; (e) C2.8

圖3給出了均勻態(tài)(VCoNi)100-x C x (x=0，0.1，0.4，1和2.8)樣品的EDS面掃分布圖 圖3a~b表明，C0和C0.1樣品中的V、Co和Ni原子分布均勻 圖3c~e表明，C0.4、C1和C2.8樣品中的V和C原子明顯富集，且主要集中在第二相，為釩碳化合物

圖3



圖3均勻態(tài)(VCoNi)100-x C x (x=0，0.1，0.4，1和2.8)的EDS面掃分布

Fig.3EDS element distribution of as-homogenized samples (a) C0; (b) C0.1; (c) C0.4; (d) C1; (e) C2.8

圖4給出了均勻態(tài)(VCoNi)100-x C x (x=0，0.1，0.4，1和2.8)的EBSD圖 圖4a2~d2表明，C0、C0.1和C0.4均為FCC單相結(jié)構(gòu)，而C1和C2.8樣品為FCC+HCP雙相結(jié)構(gòu) 在C0、C0.1和C0.4樣品中出現(xiàn)大量的(60°<111>)退火孿晶(圖4a3~c3) C1樣品中的退火孿晶急劇減少(圖4d3)；胞狀晶內(nèi)部出現(xiàn)大量的小角度晶界，表明胞狀晶內(nèi)存在較高的應(yīng)力 C2.8樣品中的退火孿晶基本消失，在胞狀晶區(qū)也能出現(xiàn)大量的小角度晶界(圖4e3)

圖4



圖4均勻態(tài)(VCoNi)100-x C x (x=0, 0.1, 0.4, 1和2.8)的EBSD圖

Fig.4EBSD of as-homogenized samples (VCoNi)100-x C x (x=0, 0.1, 0.4, 1 and 2.8) (a~e). inverse pole figure (a1~e1); phase maps (a2~e2) and grains boundary maps(a3~e3)

圖5給出了均勻態(tài)(VCoNi)100-x C x (x=0，0.1，0.4，1和2.8)的取向分布函數(shù)截面圖，ODF圖以φ2=45°、65°和90°截面圖顯示，其主要織構(gòu)成分的體積分?jǐn)?shù)在圖6中給出 圖5a表明，C0樣品含有G/B織構(gòu)組分(9.24%)和Cu織構(gòu)組分(10.4%) 圖5b表明，C0.1樣品中的Brass織構(gòu)的體積分?jǐn)?shù)明顯增大(12.7%)、S織構(gòu)組分稍有增加(7.88%)，而其他組分有所減少 圖5c表明，C0.4樣品中的S織構(gòu)大幅增強(qiáng)(13.7%)，表現(xiàn)出以Brass和G/B織構(gòu)組分為主的α取向線特征 圖5a~c表明，隨著C含量的提高，均勻態(tài)樣品的織構(gòu)逐漸向α取向線上聚集(即取向線φ1=0°→90°、φ=45°、φ2=90°)，但是強(qiáng)度降低(從6.6 mrd降至2.36 mrd) 圖5d~e表明，C1和C2.4樣品中未出現(xiàn)典型織構(gòu)類(lèi)型

圖5



圖5均勻態(tài)(VCoNi)100-x C x (x=0, 0.1, 0.4, 1和2.8)的ODF圖(φ2=45°、65°和90°截面)

Fig.5φ2=45°, 65° and 90° sections of ODF for the as-homogenized samples (a) C0; (b) C0.1; (c) C0.4; (d) C1; (e) C2.8

圖6



圖6均勻態(tài)樣品中主要織構(gòu)組分的體積分?jǐn)?shù)隨C含量的變化

Fig.6Volume fractions of main texture components in as-homogenized samples with different C contents

圖7給出了再結(jié)晶態(tài)(VCoNi)100-x C x (x=0，0.1和0.4)樣品的SEM形貌(C1和C2.8樣品因在熱壓縮過(guò)程中提前斷裂，不適合制備再結(jié)晶樣品) 可以看出，再結(jié)晶態(tài)樣品的晶粒形態(tài)均呈等軸狀，出現(xiàn)大量的板條組織，其平均晶粒尺寸分別約為5.02 μm(圖7a)、4.79 μm(圖7b)和4.22 μm(圖7c) 隨著C含量的提高，顯著析出了第二相顆粒 圖8給出了再結(jié)晶態(tài)(VCoNi)100-x C x (x=0，0.1和0.4)樣品的EBSD圖 圖8a2~c2(相圖)表明，再結(jié)晶態(tài)樣品均呈FCC單相結(jié)構(gòu)，圖中的白色區(qū)域?yàn)榈诙嗟奈恢?在圖8a3~c3(晶界圖)中可觀察到高比例的退火孿晶(60°<111>)，其比例分別為46.3%、59.1%和55.2%

圖7



圖7再結(jié)晶態(tài)(VCoNi)100-x C x (x=0, 0.1和0.4)的SEM照片

Fig.7SEM images of microstructure for the as-recrystallized samples (a) C0; (b) C0.1;(c) C0.4

圖8



圖8再結(jié)晶態(tài)(VCoNi)100-x C x (x=0, 0.1和0.4)的EBSD圖

Fig.8EBSD maps of as-recrystallized (VCoNi)100-x C x (x=0, 0.1 and 0.4) samples in (a~c), respectively (a1~c1) IPF maps; (a2~c2) phase maps; (a3~c3) GB maps

圖9給出了(VCoNi)100-x C x (x=0，0.1和0.4)再結(jié)晶樣品在φ2=45°、60°和90°截面取向分布函數(shù)圖 φ2=90°圖顯示，三種樣品的織構(gòu)均在α線上聚集，織構(gòu)最強(qiáng)點(diǎn)均在α取向線上 φ2=45°圖顯示，樣品中出現(xiàn)明顯Cu織構(gòu)組分 根據(jù)φ2=65°織構(gòu)圖，可得到樣品均存在一定量的S織構(gòu) 圖10統(tǒng)計(jì)了再結(jié)晶態(tài)樣品主要織構(gòu)組分的體積分?jǐn)?shù) 結(jié)果表明，C0樣品中的Brass和G/B為體積分?jǐn)?shù)最高的織構(gòu)組分，其比例分別為16.2%和16%，S織構(gòu)組分占14.2% C0.1樣品的G/B和Cu織構(gòu)組分增強(qiáng)，其體積分?jǐn)?shù)分別為18.4%和14.3% C0.4樣品的α取向線上各組分的體積分?jǐn)?shù)都減小，Cu和S織構(gòu)組分減小而隨機(jī)織構(gòu)增強(qiáng)

圖9



圖9再結(jié)晶態(tài)(VCoNi)100-x C x (x=0, 0.1和0.4)的ODF圖(φ2=45°、65°和90°截面)

Fig.9φ2=45°, 65° and 90° sections of the ODFs (determined by EBSD) of as-recrystallized C0 sample in (a), C0.1 sample in (b), C0.4 sample in (c)

圖10



圖10再結(jié)晶態(tài)樣品中主要織構(gòu)組分的體積分?jǐn)?shù)隨C含量的變化

Fig.10Volume fractions of main texture components in as-recrystallized samples with different C contents

圖11a給出了再結(jié)晶態(tài)(VCoNi)100-x C x (x=0，0.1和0.4)樣品的室溫拉伸曲線，表1列出了屈服強(qiáng)度、抗拉強(qiáng)度和延伸率的具體數(shù)值，其中C0.1表現(xiàn)出最優(yōu)的強(qiáng)韌化性能 圖11b表明，樣品的拉伸曲線均呈現(xiàn)出典型的三段式加工硬化率 第一階段，加工硬化率下降，塑性變形由位錯(cuò)滑移主導(dǎo)，動(dòng)態(tài)回復(fù)引起的位錯(cuò)塞積速率降低，使加工硬化率減小 此時(shí)，C0.1和C0.4樣品的加工硬化率略高于C0樣品 第二階段，加工硬化率的下降減緩，三種樣品呈現(xiàn)出近似的加工硬化率 第三階段的加工硬化率曲線均隨著真應(yīng)變的增加而急劇下降，直至斷裂

圖11



圖11再結(jié)晶態(tài)(VCoNi)100-x C x (x=0, 0.1和0.4)的室溫拉伸曲線和斷口形貌

Fig.11representative tensile engineering stress-strain curves(a); corresponding strain-hardening rate curves (b); fracture surfaces of as-recrystallized C0, C0.1 and C0.4 samples are shown in (c), (d) and (e)

Table 1

表1

表1(VCoNi)100-x C x 中熵合金的屈服強(qiáng)度、抗拉強(qiáng)度以及延伸率

Table 1Yield strength, ultimate tensile strength and elongation of (VCoNi)100-x C x medium entropy alloy

	Yield Strength / MPa	Ultimate tensile strength / MPa	Elongation / %
C0	528.30	1003.29	54.23
C0.1	744.62	1193.86	39.25
C0.4	686.68	1130.22	39.37

圖11c1~f1表明，樣品均出現(xiàn)明顯的縮頸現(xiàn)象且斷口形貌均由分布均勻的韌窩組成，為典型的韌性斷裂 圖11c表明，C0樣品的斷口有大量的韌窩，其尺寸大且比較深，表明其具有較好的塑性 而含C樣品斷口的形貌發(fā)生了變化：第一，韌窩的深度和尺寸減小(圖11c3~e3)；第二，斷口的部分區(qū)域出現(xiàn)了解理小平面(圖11d2~e2，黑色箭頭)；第三，在C0.1樣品的韌窩中心可觀察到第二相顆粒(圖11d3~e3，紅色區(qū)域) 由此可見(jiàn)，樣品斷口形貌的特征與其拉伸力學(xué)性能匹配，韌窩深度和尺寸的減小以及解理小平面的出現(xiàn)，都意味著塑性的降低

圖12給出了再結(jié)晶態(tài)(VCoNi)100-x C x (x=0，0.1和0.4)樣品在干摩擦條件下的摩擦磨損性能和磨痕形貌 圖12a(摩擦系數(shù)曲線)表明，所有曲線都顯示出類(lèi)似的兩階段(磨合和穩(wěn)態(tài))摩擦行為 在第一次磨合階段，由于磨損表面的損傷和接觸面積的增大，摩擦曲線很快到達(dá)最高點(diǎn)然后迅速下降，接著摩擦系數(shù)隨著滑動(dòng)時(shí)間的增加而逐漸增大 圖12a顯示出C0.1樣品摩擦曲線很快進(jìn)入平直階段(約2.8 min)，表明該樣品很快進(jìn)入穩(wěn)定摩擦階段，而C0和C0.4樣品則需要較長(zhǎng)的磨合期(分別約3.7和4.5 min)才能進(jìn)入穩(wěn)定摩擦階段 圖12b表明，添加C原子的VCoNi合金，其摩擦系數(shù)的變化趨勢(shì)沒(méi)有明顯的差異，但是其平均摩擦系數(shù)增大(穩(wěn)定期)而磨損率降低 三維磨損表面的形貌(圖12d1~f1)表明，C0.1和C0.4樣品的磨痕寬度比C0樣品的小 從磨痕中心區(qū)域的截面二維輪廓圖(圖12c)可見(jiàn)，磨痕寬度分別為1.006 mm(C0樣品)、0.986 mm(C0.1樣品)和0.911 mm(C0.4樣品)，磨痕平均深度分別為6.482 μm(C0樣品)、5.482 μm(C0.1樣品)和5.587 μm(C0.4樣品) 這表明，添加C原子使VCoNi中熵合金的耐磨性能提高

圖12



圖12再結(jié)晶態(tài)(VCoNi)100-x C x (x=0, 0.1和0.4)的摩擦磨損性能和磨痕形貌

Fig.12Real time friction coefficient (a); average friction coefficient and wear rate (b); wear scar profile (c); wear scar morphology of as-recrystallized C0 sample (d), C0.1 sample (e) and C0.4 sample (f)

圖12d~f(磨痕形貌)表明，三種再結(jié)晶態(tài)樣品的磨損表面均由犁溝和磨屑組成 圖12d2~d3表明，C0樣品的磨痕分為黑色氧化區(qū)和灰色未氧化區(qū)，磨痕表面有明顯的與滑動(dòng)方向相同的犁溝型劃痕以及在部分區(qū)域出現(xiàn)一些黑色大塊氧化膜、細(xì)小的麻點(diǎn)以及小型的魚(yú)鱗片狀碎片 這表明，基體樣品的磨損機(jī)制屬于氧化磨損、磨粒磨損和粘著磨損 圖12e2表明，C0.1樣品表面的犁溝型劃痕變淺，磨粒磨損的作用減弱；而磨痕表面黑色區(qū)域增大(圖12e3)，樣品磨損產(chǎn)生的氧化增加，魚(yú)鱗片狀碎片明顯增多，表明氧化磨損和粘著磨損的作用加強(qiáng) 由此可見(jiàn)，C0.1樣品的磨損機(jī)制為磨粒磨損、氧化磨損和粘著磨損 圖12f表明，C0.4樣品的磨痕表面形貌與C0.1樣品基本相同，但是黑色區(qū)域增大和魚(yú)鱗片狀碎片明顯增加(圖12f3)，表明C0.4樣品的磨損機(jī)制仍為磨粒磨損、氧化磨損和粘著磨損

3 討論

添加不同含量的C影響VCoNi合金的微觀組織 第一，C0、C0.1和C0.4均勻態(tài)樣品中(圖2a~c)的晶粒形態(tài)為等軸晶組織和板條狀的退火孿晶；而C1均勻態(tài)樣品中(圖2d)的晶粒形態(tài)為胞狀晶，C2.8樣品中(圖2e)的晶粒形態(tài)為胞狀晶 生成胞狀晶的原因是，添加過(guò)多的C原子導(dǎo)致HCP相的生成(圖1) 第二，隨著C含量的提高，V和C原子明顯富集(圖3) 其原因是，在快速冷卻過(guò)程中C和V極強(qiáng)的親和力[29]使其極易生成釩碳化合物析出相 同時(shí)，隨著C含量的提高，釩碳化合物增加 第三，含C再結(jié)晶態(tài)樣品的晶粒發(fā)生了細(xì)化，主要與第二相有關(guān) 在退火過(guò)程中第二相對(duì)晶界的釘扎抑制了再結(jié)晶晶粒的長(zhǎng)大[30]

含C再結(jié)晶樣品的屈服強(qiáng)度和抗拉強(qiáng)度均提高(圖11a，b)，而塑性略有降低 其主要原因是：第一，在VCoNi固溶體系中的C提供了間隙強(qiáng)化 第二，部分在晶界處析出的第二相使晶界界面能降低，降低了晶粒長(zhǎng)大驅(qū)動(dòng)力[31]，導(dǎo)致晶粒細(xì)化(圖8a1~c1)而產(chǎn)生了細(xì)晶強(qiáng)化 第三，晶界處C原子的偏聚引起晶界內(nèi)聚力增大，沿晶斷裂分?jǐn)?shù)的減小有助于穩(wěn)定韌性[32]，從而使含C樣品斷口的形貌仍舊以韌窩形貌為主(圖11c~e) 因此，C0.1和C0.4樣品的屈服強(qiáng)度和抗拉強(qiáng)度顯著提高 但是，C含量為0.4的樣品其屈服強(qiáng)度和抗拉強(qiáng)度呈下降趨勢(shì)，表明再結(jié)晶態(tài)C0.1樣品中第二相的形態(tài)和尺寸均已達(dá)到最佳，從而使樣品具有優(yōu)異的強(qiáng)韌化綜合力學(xué)性能

添加C原子樣品的摩擦磨損能力更高，可歸因于兩個(gè)方面的原因 第一，含C樣品在晶界處析出的硬質(zhì)釩碳化合物，提高了樣品的硬度從而增強(qiáng)了粘著磨損行為 第二，頻繁的氧化磨損使含C樣品表面在高速摩擦過(guò)程中迅速氧化，生成的氧化物黏著在摩擦表面 時(shí)間越長(zhǎng)則氧化層越厚，產(chǎn)生的潤(rùn)滑作用降低了樣品的磨損率，從而使樣品的耐磨性能提高

4 結(jié)論

(1) x=0~1的(VCoNi)100-x C x 熵合金均勻態(tài)樣品中的晶粒形態(tài)為等軸晶，且出現(xiàn)退火孿晶，隨著C含量的提高，晶粒尺寸減小，呈顆粒狀的第二相的含量提高；在x≥1的樣品中出現(xiàn)了粗大的胞晶，第二相呈現(xiàn)多形態(tài)特征，退火孿晶減少 再結(jié)晶態(tài)樣品中晶粒的形態(tài)均呈等軸晶狀，隨著C含量的提高，晶粒尺寸減小，第二相的含量提高

(2) 均勻態(tài)C0樣品以G/B和Cu織構(gòu)為主，C0.1樣品Brass織構(gòu)的體積分?jǐn)?shù)明顯增大，C0.4樣品具有以Brass和G/B織構(gòu)組分為主的α取向線特征，在C1和C2.4樣品中未出現(xiàn)典型織構(gòu)類(lèi)型 再結(jié)晶態(tài)樣品均表現(xiàn)出在α線上聚集，且織構(gòu)最強(qiáng)點(diǎn)均在α取向線上

(3) C0.1再結(jié)晶態(tài)樣品具有最優(yōu)的強(qiáng)韌化性能，因?yàn)檫m量的C原子使第二相的形態(tài)和尺寸均達(dá)到最佳，實(shí)現(xiàn)了細(xì)晶強(qiáng)化、間隙強(qiáng)化和第二相強(qiáng)化

(4) 含C原子的再結(jié)晶樣品的摩擦磨損性能提高，因?yàn)镃原子生成的釩碳化合物增強(qiáng)了粘著磨損和氧化磨損，減弱了磨粒磨損，生成的氧化層減少了樣品的磨損

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