離子氮鋁共滲方法及對(duì)42CrMo鋼組織性能的影響

康前飛，楊衛(wèi)民，魏坤霞，汪丹丹，劉細(xì)良，胡靜,2

離子氮鋁共滲方法及對(duì)42CrMo鋼組織性能的影響

康前飛1a,2，楊衛(wèi)民1b,3，魏坤霞1a,2，汪丹丹1a,1b，劉細(xì)良1a,1b，胡靜1a,1b,2

（1.常州大學(xué) a.江蘇省材料表面科學(xué)與技術(shù)重點(diǎn)實(shí)驗(yàn)室 b.材料科學(xué)與工程國(guó)家級(jí)實(shí)驗(yàn)教學(xué)示范中心，江蘇 常州 213164；2.常州大學(xué) 懷德學(xué)院，江蘇 靖江 214500； 3.常州賽斐斯新材料科技有限公司，江蘇 常州 213164）

研發(fā)離子氮鋁共滲試驗(yàn)方法，達(dá)到不影響42CrMo鋼基體組織性能前提下，顯著提高試樣表面硬度和耐磨性效果。采用電解法在42CrMo鋼表面沉積氫氧化鋁膜，再在520 ℃/4 h工藝下進(jìn)行離子氮鋁共滲處理，并在相同工藝參數(shù)條件與傳統(tǒng)離子滲氮進(jìn)行對(duì)比。用光學(xué)顯微鏡、維氏顯微硬度計(jì)、摩擦磨損測(cè)試機(jī)、X射線衍射儀及SEM對(duì)截面顯微組織、截面硬度、耐磨性及物相等進(jìn)行了測(cè)試和分析。獲得了離子氮鋁共滲試驗(yàn)方法，在520 ℃/4 h相同工藝參數(shù)下，離子氮鋁共滲形成的化合物層和有效硬化層厚度比常規(guī)離子滲氮顯著增加，其中，化合物層厚度由17.24 μm增加到52.13 μm，有效擴(kuò)散層從175 μm增加到1 050 μm，相當(dāng)于等離子處理效率提升6倍；同時(shí)，滲層形成了AlN及FeAl強(qiáng)化相，大幅度提高了滲層的硬度及耐磨性能。表面硬度由750HV0.025提高到1 250HV0.025，摩擦因數(shù)由常規(guī)離子滲氮0.52下降到0.29，磨損率由常規(guī)離子滲氮3.22×10?5g/(m·N)下降到1.21×10?5g/(m·N)，磨痕明顯減輕。采用電解硝酸鋁生成氫氧化鋁沉淀附著在工件表面作為預(yù)處理，獲得了離子氮鋁共滲試驗(yàn)方法，與常規(guī)離子滲氮相比，離子氮鋁共滲形成了多層次滲層結(jié)構(gòu)，大幅度提高常規(guī)離子處理效率、表面硬度及耐磨性。

42CrMo鋼；離子滲氮；氮鋁共滲；耐磨性；摩擦因數(shù)；電沉積

離子滲氮是一種應(yīng)用較為廣泛的化學(xué)熱處理方法，具有環(huán)保清潔等特點(diǎn)，可提升工件試樣表面硬度及耐磨性[1-6]。但是常規(guī)離子滲氮處理的保溫時(shí)間較長(zhǎng)，在工件承受重載沖擊或磨損時(shí)，因?yàn)榛衔飳哟嘈暂^大，易在工件表面出現(xiàn)化合物層局部開(kāi)裂和脫落，導(dǎo)致零部件性能過(guò)早失效，降低工件預(yù)期服役壽命[7-11]。

已有的研究表明，添加微量合金元素可以改善常規(guī)離子滲氮滲層組織和性能，如添加微量硼離子滲氮，化合物層中可形成高硬度硼化物，使耐磨性能大幅度提升[12-15]；添加微量硫可在化合物層形成硫化物，達(dá)到減小摩擦因數(shù)及提升抗擦傷能力的效果[16]；添加微量鈦可改善滲層特性，提升滲層沖擊韌性[17]。

基于Al可與N和Fe結(jié)合形成性能優(yōu)良的AlN及FeAl相，特別是AlN具有高硬度、高耐磨、低摩擦因數(shù)，以及磨損時(shí)具有自潤(rùn)滑能力，因此可以預(yù)期：添加微量鋁有可能對(duì)離子滲氮效果產(chǎn)生顯著提升作用[18-20]。但是，由于鋁的熔點(diǎn)較低，無(wú)法像其他合金元素一樣直接放入離子滲氮爐里，實(shí)現(xiàn)離子氮鋁共滲。因此，設(shè)計(jì)新型離子共滲試驗(yàn)方法是實(shí)現(xiàn)離子氮鋁共滲技術(shù)的必要手段。

本研究首次探索采用電解硝酸鋁生成氫氧化鋁沉淀附著在工件表面作為預(yù)處理，進(jìn)行離子氮鋁共滲。目的是研究離子氮鋁共滲對(duì)42CrMo鋼組織性能的影響。研究結(jié)果表明，該方法成功實(shí)現(xiàn)了離子氮鋁共滲，且比傳統(tǒng)離子滲氮效率和性能都得到顯著提高。

1 試驗(yàn)

材料使用為調(diào)質(zhì)態(tài)42CrMo鋼，基體硬度為370HV0.025，化學(xué)成分（以質(zhì)量分?jǐn)?shù)計(jì)）為：0.39% C，0.89% Cr，0.77% Mn，0.28% Si，0.21% Mo，其余為Fe。用線切割加工成10 mm×10 mm×5 mm的試樣，并采用180#—1500#的砂紙逐一進(jìn)行打磨，然后將樣品放在無(wú)水乙醇中用超聲波清洗5 min去除雜質(zhì)。采用文獻(xiàn)中報(bào)道的電解法在試樣表面沉積氫氧化鋁膜[21]，具體過(guò)程為：將試樣接在型號(hào)為ITECH- IT6721直流電源器陰極，陽(yáng)極為純鋁；然后放入質(zhì)量濃度為30 g/L的硝酸鋁溶液中，調(diào)節(jié)電流密度為6 mA/cm2進(jìn)行電解；工作電壓為3 V，工作電流為0.024 A，電解時(shí)間為10 min。將沉積氫氧化鋁試樣取出吹干后放入離子滲氮爐中，在520 ℃/4 h下進(jìn)行離子氮鋁共滲。為進(jìn)行對(duì)比研究，在相同工藝參數(shù)（520 ℃/4 h）下對(duì)42CrMo鋼進(jìn)行常規(guī)離子滲氮。

等離子處理后，用DMI-3000M型號(hào)光學(xué)顯微鏡對(duì)工件試樣的橫截面組織及表面磨痕形貌進(jìn)行觀察。用D/max-2500型號(hào)X射線衍射儀對(duì)工件試樣物相組成進(jìn)行測(cè)試分析，使用射線為Cu-Kα射線，波長(zhǎng)=1.54×10?10m，掃描速率為0.2 (°)/min，其步寬設(shè)定為0.02°，2角度為20°～100°。顯微硬度使用型號(hào)為HXD-1000TMC維氏硬度計(jì)對(duì)工件橫截面硬度進(jìn)行測(cè)量，載荷為25 g，壓力保持時(shí)間15 s。用型號(hào)為MMV-1A多功能材料摩擦磨損測(cè)試儀測(cè)量工件試樣耐磨性。對(duì)磨材料用GCr15鋼球，直徑為5 mm，轉(zhuǎn)速為214 r/min，使用加載載荷為200 g，進(jìn)行對(duì)磨時(shí)間為15 min。用MST-5000電子天平對(duì)磨損前后質(zhì)量差進(jìn)行測(cè)量，計(jì)算磨損量。采用SEM觀察表面形貌。

2 結(jié)果及分析

2.1 氫氧化鋁鍍膜形貌

圖1為試樣通過(guò)電解硝酸鋁沉積氫氧化鋁膜的表面形貌。從圖中可以看出，在工件表面出現(xiàn)大量微小氫氧化鋁碎塊，并且相鄰碎塊之間存在間隙，這些間隙可以很好地將濺射到試樣表面的氮原子和鋁原子吸附在工件表面并向內(nèi)擴(kuò)散。

圖1 電解硝酸鋁沉積氫氧化鋁膜的表面形貌

2.2 滲層橫截面顯微組織

圖2為相同工藝參數(shù)（520 ℃/4 h）下等離子處理后試樣截面顯微組織?？梢钥闯?，離子氮鋁共滲（PNAl）處理后，化合物層顯微形貌不同于常規(guī)離子滲氮，形成了圖2a所示的多層次滲層組織，如同大鋸齒型狀牢牢釘在試樣基體中，同時(shí)化合物層厚度大幅度提高，由常規(guī)離子滲氮的17.24 μm顯著增厚到52.13 μm。

2.3 XRD分析

圖3為相同工藝參數(shù)（520 ℃/4 h）下等離子處理后物相分析圖（XRD）。從圖中可以看出，離子氮鋁共滲（PNAl）處理后出現(xiàn)了AlN及FeAl相，且γ'-Fe4N和ε-Fe2～3N衍射峰比離子滲氮（PN）時(shí)降低，說(shuō)明離子氮鋁共滲層中γ'-Fe4N和ε-Fe2～3N含量減少。

2.4 截面硬度

圖4為相同工藝參數(shù)（520 ℃/4 h）下等離子處理后試樣截面硬度。可以看出，離子氮鋁共滲（PNAl）處理后，試樣表層硬度遠(yuǎn)高于常規(guī)離子滲氮（PN）處理，表面硬度由750HV0.025提高到1 250HV0.025；有效硬化層由175 μm顯著增加到1 050 μm，相當(dāng)于等離子處理效率提升6倍。圖4中可見(jiàn)，離子氮鋁共滲（PNAl）和離子滲氮（PN）處理后，表面硬度比基體硬度375HV0.025分別提升了875HV0.025和375HV0.025。

圖2 相同工藝參數(shù)（520 ℃/4 h）下等離子處理后截面顯微組織

圖3 相同工藝參數(shù)（520 ℃/4 h）下離子氮鋁共滲（PNAl）和離子滲氮（PN）處理后物相分析

圖4 相同工藝參數(shù)（520 ℃/4 h）下離子氮鋁共滲（PNAl）和離子滲氮（PN）截面硬度

2.5 耐磨性分析

圖5為相同工藝參數(shù)（520 ℃/4 h）下等離子處理后的摩擦因數(shù)?？梢钥闯?，離子氮鋁共滲處理后，試樣摩擦因數(shù)為0.29，明顯低于常規(guī)離子滲氮處理的0.52，且離子氮鋁共滲處理試樣的摩擦因數(shù)曲線較平滑，波動(dòng)幅度較小。

圖5 相同工藝參數(shù)（520 ℃/4 h）下等離子處理后摩擦因數(shù)對(duì)比

圖6為相同工藝參數(shù)（520 ℃/4 h）下等離子處理后的磨痕形貌。可以看出，離子氮鋁共滲試樣表面磨損凹坑較小，只出現(xiàn)較細(xì)的磨槽，且表面破碎痕跡較少。常規(guī)離子滲氮試樣磨痕較寬，且磨損表面有較大凹坑和磨損物產(chǎn)生，導(dǎo)致摩擦因數(shù)曲線波動(dòng)較大，見(jiàn)圖5。

為進(jìn)一步評(píng)估氮鋁共滲與常規(guī)離子滲氮試樣的耐磨性，根據(jù)式（1）所示的比磨損率計(jì)算方法[22]進(jìn)行了量化對(duì)比分析。

=Δ/() (1)

式中：Δ為工件磨損前后質(zhì)量損失差（g）；為施加荷載大?。∟）；為滑動(dòng)距離（m）。計(jì)算結(jié)果如圖7所示，從圖中可以看出，氮鋁共滲試樣磨損率顯著降低，由常規(guī)離子滲氮試樣的3.22×10?5g/(m·N)下降到1.21×10?5g/(m·N)，即耐磨性提高約2.7倍。

圖6 相同工藝參數(shù)（520 ℃/4 h）下等離子處理后磨痕形貌對(duì)比

圖7 相同工藝參數(shù)（520 ℃/4 h）下等離子處理后磨損率與表面硬度對(duì)比

2.6 表面SEM-EDS分析

試樣在相同工藝參數(shù)（520 ℃/4 h）下等離子處理后的表面形貌見(jiàn)圖8?？梢?jiàn)，離子氮鋁共滲（圖8a）后表面顆粒不但細(xì)小且均勻，表面粗糙度相對(duì)于常規(guī)離子滲氮較??；而常規(guī)離子滲氮（圖8b）后表面顆粒均勻性較差，且存在大顆粒突起，這些較大的突起相當(dāng)于堅(jiān)硬磨粒，會(huì)導(dǎo)致摩擦因數(shù)的波動(dòng)性較大，見(jiàn)圖4。在磨損過(guò)程中會(huì)從黏著磨損變成為磨粒磨損，這將顯著增加對(duì)磨材料與樣品間的磨損程度，導(dǎo)致試樣表面在磨損時(shí)形成大量拉傷及劃傷，使耐磨性大幅降低[23-25]，見(jiàn)圖5。表面元素含量EDS分析結(jié)果見(jiàn)表1—2，可見(jiàn)，離子氮鋁共滲后表面鋁元素含量達(dá)到10.32%；同時(shí)氮元素含量由常規(guī)離子滲氮12.53%提升到16.93%，表面氮濃度的提高可能源于強(qiáng)氮化物形成元素鋁的吸引效果，高氮濃度有利于滲層的快速形成。

圖8 相同工藝參數(shù)（520 ℃/4 h）下等離子處理后試樣表面形貌及元素含量（SEM-EDS）

表1 離子氮鋁共滲EDS元素分布

表2 常規(guī)離子滲氮EDS元素分布

3 分析與討論

離子氮鋁共滲與常規(guī)離子滲氮試樣組織性能對(duì)比總結(jié)見(jiàn)表3?？梢?jiàn)，試樣離子氮鋁共滲（PNAl）處理的效率、表層硬度及耐磨性都遠(yuǎn)遠(yuǎn)優(yōu)于常規(guī)離子滲氮（PN）處理，且表面形成了圖8所示的細(xì)小均勻分布的微米顆粒。

高性能離子氮鋁共滲層高效形成機(jī)理可能是：沉積在試樣表面的微小塊狀A(yù)l(OH)3之間產(chǎn)生大量微裂紋，極大地提升了試樣表面粗造度，有利于吸附轟擊試樣的氮原子，提高氮原子濃度，使氮原子擴(kuò)散能力提升[26-27]。Al(OH)3在高溫時(shí)分解成孔縫狀A(yù)l2O3和游離態(tài)H2O；游離態(tài)H2O與Fe反應(yīng)生成Fe3O4，從而在工件表面形成孔洞，孔縫狀A(yù)l2O3和氧化孔洞都為氮原子擴(kuò)散提供大量通道[28]，從而提高氮原子擴(kuò)散速率，加速白亮層形成；使離子氮鋁共滲層硬度顯著高于傳統(tǒng)離子滲氮。同時(shí)，因離子氮鋁共滲處理后滲層中形成了圖2所示的高硬度AlN及FeAl相[29-30]，使表面硬度及有效硬化層顯著提高。

表3 離子氮鋁共滲與常規(guī)離子滲氮對(duì)比

4 結(jié)論

1）離子氮鋁共滲處理比常規(guī)離子滲氮效率明顯提高，化合物層厚度由17.24 μm增加到52.13 μm，有效擴(kuò)散層從175 μm增加到1 050 μm，相當(dāng)于離子處理效率提升約6倍。

2）離子氮鋁共滲處理后滲層中形成了高硬度AlN及FeAl相，且表面顆粒細(xì)小均勻分布。

3）離子氮鋁共滲處理后表面硬度由常規(guī)離子滲氮的750HV0.025提高至1 250HV0.025，提升了500HV0.025。離子氮鋁共滲處理和離子滲氮處理后，表面硬度比基體硬度375HV0.025分別提升了875HV0.025和375HV0.025。

4）離子氮鋁共滲處理后試樣表面的耐磨性顯著提高，摩擦因數(shù)由常規(guī)離子滲氮的0.52下降到0.29；磨痕較淺較窄；磨損率由3.22×10?5g/(m·N)下降到1.21×10?5g/(m·N)，相當(dāng)于耐磨性提高到常規(guī)離子滲氮的2.7倍。

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Development of a Novel Plasma Aluminum-nitriding Methodology and Its Effect on the Microstructure and Properties for 42CrMo Steel

1a,2,1b,3,1a,2,1a,1b,1a,1b,1a,1b,2

(1. a. Jiangsu Key Laboratory of Materials Surface Science and Technology, b. National Experimental Demonstration Center for Materials Science and Engineering, Changzhou University, Jiangsu Changzhou 213164, China; 2. Huaide College, Changzhou University, Jiangsu Jingjiang 214500, China; 3. Changzhou Surface Advanced Materials Technology Co., Ltd., Jiangsu Changzhou 213164, China)

Plasma nitriding is a widely used environment friendly chemical heat treatment, which can effectively improve the surface layer hardness, wear resistance and corrosion resistance of metal components. Unfortunately, it is hard to meet the advanced technical requirements of very high efficiency and excellent performances proposed by some cooperative enterprises. To meet the advanced technical requirements, conventional plasma nitriding is necessary to be promoted. It has been reported that titanium-enhanced plasma nitriding has much high efficiency and better performance than that of conventional plasma nitriding. Since Aluminum can react with both nitrogen and iron to form very hard AlN and FeAl compounds, it can be supposed that Aluminun-enhanced plasma nitriding may have better performances than that of titanium-enhanced plasma nitriding. However, since Aluminun has much lower melting point, Aluminun-enhanced plasma nitriding, also called plasma aluminum-nitriding, can not be conducted by putting Aluminun sheet or particles in the furnace during plasma nitriding, as was performed during titanium-enhanced plasma nitriding. Therefore, the novel method to carry out plasma aluminum-nitriding was primarily explored and developed in this research. And the effect of the novel plasma aluminum-nitriding technology on the efficiency and properties were systematically investigated. The novel plasma aluminum-nitriding in this research was consisted of the following two steps: firstly, Aluminum hydroxide film was deposited on 42CrMo steel by electrolysis; secondly, plasma aluminum-nitriding was carried out at 520 ℃/4 h. Meanwhile, conventional plasma nitriding was conducted under the same conditions as a reference. Optical microscope, X-ray diffractometer, Vickers microhardness tester, friction and wear tester and SEM were used to test and analyze the microstructure, phase, hardness and wear resistance of the cross section. The results showed that at the same process parameter of 520 ℃/4 h, a multi-layer structure was formed; the thickness of compound layer and effective hardening layer by plasma aluminum-nitriding was significantly higher than that by conventional plasma nitriding. The thickness of compound layer increased from 17.24 μm to 52.13 μm, and the effective diffusion layer increased from 175 μm to 1 050 μm, it was equivalent to 6 times increase in plasma treating efficiency. Meanwhile, AlN and FeAl phases were formed in the surface layer, which resulted in great enhancement of hardness and wear resistance of the samples, the surface hardness increased from 750HV0.025 to 1 250HV0.025, the friction coefficient decreased from 0.52 to 0.29, the wear rate decreased from 3.22×10?5g/(m·N) to 1.21×10?5g/(m·N), and the wear marks are obviously reduced. In all, novel plasma aluminum-nitriding technology was primarily developed by using electrolytic aluminum nitrate to generate aluminum hydroxide precipitation on the surface of samples as a pretreatment. Plasma treating efficiency, surface hardness and wear resistance was dramatically enhanced by the novel plasma aluminum-nitriding technology due to the formation of multi-layer structure.

42CrMo steel; plasma nitriding; plasma aluminum-nitriding; wear resistance; friction coefficient; electrodeposition

TG156.8+2

A

1001-3660(2023)01-0394-07

10.16490/j.cnki.issn.1001-3660.2023.01.040

2021–12–24；

2022–04–09

2021-12-24；

2022-04-09

國(guó)家自然科學(xué)基金（21978025、51774052）；江蘇省第三期優(yōu)勢(shì)學(xué)科建設(shè)項(xiàng)目（PAPD-3）；江蘇高校品牌專(zhuān)業(yè)建設(shè)工程資助項(xiàng)目（TAPP）；常州科技項(xiàng)目（CJ20210114）；江蘇省研究生創(chuàng)新基金項(xiàng)目（CX10292）

The National Natural Science Foundation of China (21978025, 51774052); Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD-3); Top-notch Academic Program Projects of Jiangsu Higher Education Institutions (TAPP); Science and Technology Project of Changzhou City (CJ20210114); Postgraduate Research & Practice Innovation Program of Jiangsu Province (CX10292)

康前飛（1997—），男，碩士研究生，主要研究方向?yàn)楸砻婀こ獭?/p>

KANG Qian-fei (1997-), Male, Postgraduate, Research focus: surface engineering.

胡靜（1966—），女，博士，教授，主要研究方向?yàn)榻饘俨牧媳砻娓男浴?/p>

HU Jing (1966-), Female, Ph. D., Professor, Research focus: surface modification for metals.

康前飛, 楊衛(wèi)民, 魏坤霞, 等.離子氮鋁共滲方法及對(duì)42CrMo鋼組織性能的影響[J]. 表面技術(shù), 2023, 52(1): 394-400.

KANG Qian-fei, YANG Wei-min, WEI Kun-xia, et al. Development of a Novel Plasma Aluminum-nitriding Methodology and Its Effect on the Microstructure and Properties for 42CrMo Steel[J]. Surface Technology, 2023, 52(1): 394-400.

責(zé)任編輯：萬(wàn)長(zhǎng)清