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选择42CrMo为基体材料。粉末为Fe06+TiC与Fe06+Mo粉末,基体与Fe06粉末的化学成分表见表 1,表 2为TiC粉末化学成分表。由于基体板材是光板,需要用砂纸在板材上面进行打磨,然后用无水乙醇清洗。因粉末是两种,所以需要对两种粉末进行混粉,混粉装置采用的是行星式球磨机。
表 1 基体与Fe06粉末化学成分表
Table 1. Substrate and Fe06 powder chemical composition list
compositions(mass fraction w) C Si Cr Ni B Mo Fe Fe06 0.008 0.02 0.0075 0.32 0.04 — balance 42CrMo 0.004~0.005 0.002~0.004 0.009~0.012 ≤0.003 — 0.002~0.003 — 表 2 TiC粉末化学成分表
Table 2. TiC powder chemical composition list
compositions(mass fraction w) Ti C Fe free carbon other impurity allowance TiC 0.802 0.195 0.001 0.001 0.003 -
准备阶段:首先将粉末放入干燥箱中,将干燥箱温度调为120 ℃烘干1 h,再将TiC/Mo粉以0, 0.10, 0.15, 0.20的质量分数分别与Fe06粉末进行配比。用超声振动清洗研磨球和罐体内部,清洗完成后进行烘干,保证研磨球以及罐体无水分即可,研磨球倒入罐体后再将称好的粉末倒入其中。
实验阶段:将研磨罐盖好放入球磨机中固定,连接电源,每30 min正反转颠倒,球磨机转速300 r/min,混粉30 min,切断电源后方可打开球磨机,再将混好的粉末与研磨球分离并将混合均匀的粉末再次放入干燥箱烘干。
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图 1为激光熔覆实验设备。由激光发生器、激光头、DPSF-2送粉器、六轴机器人、KR30HA机械臂、激光控制箱、工作台等组成。在扫描速率为3 mm/s、激光功率为1000 W、送粉率为1.4 r/min时,将不同比例的Fe06-TiC粉末(Fe06+0.10TiC,Fe06+0.15TiC,Fe06+ 0.20TiC)与Fe06-Mo粉末(Fe06+0.10Mo,Fe06+0.15Mo,Fe06+0.20Mo)混合均匀熔覆到42CrMo基体上。分析熔覆完成后的复合材料涂层的物相组成、显微组织和显微硬度,接着进行摩擦磨损测试并分析其磨损形貌及磨损机理。
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通过XRD实验检测出的相组成如图 2所示。图 2a中硬质相TiC主要有:α-Fe、Fe-Cr、Fe0.975Ti0.025以及Fe0.905Si0.095。铁基合金中的Fe、Cr、Ni元素发生反应生成CrFe4,Fe-Si和Fe-Ni相,当TiC添加后,生成新相Fe0.975Ti0.025,这是由于TiC熔融时将C元素分解,Ti与铁基合金中的Fe元素发生反应生成的。TiC质量分数的增加导致第1个衍射峰的强度逐渐降低,结晶性能下降。TiC陶瓷颗粒具有较高熔点,在激光功率,送粉率和扫描速率一致的情况下, 随着TiC含量增多,熔化所需的能量越多,所以有更多未熔的TiC硬质颗粒会滞留在涂层内增强涂层的耐磨损性能。
图 2b中(Fe、Mo)复合涂层的XRD物相主要有:α-Fe、Cr-Fe、Fe-(Ni/Si)和Fe-Mo。铁基合金与Mo元素反应生成Fe9.7Mo0.3相,极大增强了涂层的耐磨损性能。Mo元素与基体可以很好地融合,随着Mo粉质量分数增高,衍射峰的强度呈现出先降低后增高的趋势。为抑制结晶生长最高添加量,当Mo粉的质量分数超过0.15时,未熔的Mo粉与铁基合金生成Fe9.7Mo0.3相含量增多,此时衍射峰强度呈上升趋势。未熔的Mo粉弥散在熔覆层也会改善其机械性能, 增强硬度及耐磨性能。
熔覆层中无论TiC硬质颗粒或者Mo粉均与铁基合金反应生成新的增强相,具体的性能优良还需进一步讨论。
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熔覆层从下到上的晶粒凝固过程主要由形状控制因子G/R决定,G为温度梯度,R为凝固速率。在熔池底部G较大,R较小,G/R值很大,熔覆层底部的结构呈亮白色带状[21]。图 3为Fe06熔覆层的微观组织。Fe06熔覆层底部组织如图 3a所示,随着熔覆进行,G/R值减小,底部结合区向散热方向生成了粗大的柱状晶。中部组织见图 3b,表现为分布广泛的胞状晶,这是因为随着G/R值减小,晶体生长方式由平面晶逐渐过渡为胞状晶,熔覆层上部组织也会更加致密和细化。
Fe06+TiC复合熔覆层显微组织图如图 4所示。图 4a、图 4b分别为Fe06+0.10TiC复合涂层的底部组织和中部组织,图 4c、图 4d分别为Fe06+0.15TiC复合涂层的底部组织和中部组织,图 4e、图 4f分别为Fe06+0.20TiC复合涂层的底部组织和中部组织。由图 4可知,在底部结合区部分生成了柱状晶并朝着熔覆层中部延伸生长,熔覆层中部由分布均匀的等轴晶组成。可以看出,当TiC质量分数增加,熔覆层底部熔合线逐渐变宽;结合区上部的柱状晶由细长转变为粗短,中部鱼骨状树枝晶逐渐由胞状晶形态取代。熔覆层底部集合区域冷却速度慢,大量TiC在此区域发生分解反应,使得熔覆层底部强化效果不明显,随着熔覆进行,冷却速度逐渐加快,熔池中未熔的TiC颗粒嵌入到熔覆层中,使得硬度大幅提高[22]。
Fe06+Mo复合熔覆层显微组织图如图 5所示。图 5a、图 5b分别为Fe06+0.10Mo复合涂层的底部组织和中部组织; 图 5c、图 5d分别为Fe06+0.15Mo复合涂层的底部组织和中部组织; 图 5e、图 5f分别为Fe06+0.20Mo复合涂层的底部组织和中部组织。如图 5所示,熔覆层底部主要以平面晶的形式展现并逐渐演化为柱状晶和部分枝晶(鱼骨状),随着Mo粉添加量增大,平面晶生长区域变大,柱状晶由细长变得粗短,逐渐向胞状晶(花瓣状)变化,熔覆层中部组织随着Mo粉添加量增加变得更为致密和均匀,可有效提高熔覆层的性能。当Mo粉质量分数达到0.20时,熔覆层成形最好。
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磨损量和磨损率是评价材料耐磨性的指标,具体的磨损率W计算公式如下式所示[23]:
$ W=\frac{m}{\pi d n} $
(1) 式中,m为磨损量,d为对磨副直径(40 mm),n为对磨副总转动圈数。
图 6为8组试样的摩擦因数曲线图。可见,不同试样在9 min内的初始磨合阶段摩擦因数急剧增加,因为此时对磨副与涂层的接触属于微凸体接触[24], 涂层表面微凸体被挤压、剪切,产生磨粒充当硬质物对涂层表面进行磨粒磨损,9 min后微凸体被磨平进入稳定磨损阶段,磨损率在一定范围内上下波动,此时为该材料正常磨损状态。
各试样磨损率计算结果如表 3所示,磨损量如图 7所示。结合磨损量和磨损率来看,随着涂层中TiC陶瓷颗粒和Mo粉质量分数的增多,涂层的磨损量和磨损率呈下降趋势。Fe06+0.20Mo的磨损量(2.1 mg) 和磨损率(1.7408×10-6 mg·m-1)最低,耐磨性能最好,纯Fe基的磨损量为7.8 mg,约为基体磨损量的2/5,磨损也相对剧烈未能表现出较好的耐磨性能,而添加硬质颗粒和Mo粉后,耐磨性能大大提升,磨损量平均约为基体磨损量7/50,耐磨性能得到很大程度的提升。
表 3 磨损率
Table 3. Wear rate
samples substrate Fe06 0.10TiC 0.15TiC 0.20TiC 0.10Mo 0.15Mo 0.20Mo wear rate/(10-6mg·m-1) 16.2471 6.4656 3.0670 2.4039 1.9065 2.6526 2.2381 1.7408 -
图 8为各试样涂层显微硬度。由图 8可见,TiC/Mo的添加可有效改善纯铁基的显微硬度,纯Fe基涂层平均硬度约为772.71 HV0.2,随着陶瓷颗粒和Mo粉质量分数增加,硬度呈上升趋势,在Fe06+0.20TiC时,硬度达到最高,平均约为1272.22 HV0.2; Fe06+0.20Mo复合涂层平均硬度达到1040.49 HV0.2; Fe06涂层硬度较基体硬度(319.17 HV0.2)提高了2.42倍。图 9为不同涂层熔覆层与基体硬度对比图,复合涂层热影响区的硬度较基体也提高了2倍左右。TiC/Mo-Fe06涂层硬度的提高一方面得益于Cr-Fe超硬相广泛分布,Mo粉可以起到细化微观组织的作用,阻碍位错和晶界迁移很大程度强化晶体从而提高硬度;另一方面,TiC/Mo熔点较高,部分固熔于熔覆层,弥散在熔覆层中增强涂层机械性能,改善硬度和磨损性能。
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基体与Fe06涂层的磨损形貌如图 10所示。熔覆层表面有明显的呈条状的划痕和犁沟, 涂层表面有细条痕表、片状脱落现象。图 10a为基体磨损形貌图,基体试样表面发生了剧烈的磨粒磨损以及粘着磨损现象,因此基体表面呈现出密集深长的犁沟并伴有片状的涂层剥落。同样的Fe06涂层的磨损机理与基体一致,磨损现象如图 10b所示,但是基体试样的犁沟比Fe06涂层宽而深,磨损更为剧烈,磨损量更大,所以Fe06涂层耐磨性能优于基体试样[25]。
Fe06+TiC复合涂层磨损形貌图如图 11所示。Fe06+0.10TiC复合涂层微凸处发生局部塑性变形,部分材料在粘着点发生剪切断裂,形成粘着磨损,如图 11a所示,熔覆层表面有部分金属附着物在滑动过程中脱落成为磨屑,有较为强烈的磨粒磨损并引发表面裂纹最终使表层材料断裂剥落产生疲劳磨损形成小坑[26]。从图中可以看到,随着TiC陶瓷颗粒质量分数增多,涂层同样表现出粘着磨损和磨粒磨损,但涂层的片状脱落变小,细条痕变得短而浅,如图 11b、图 11c所示。说明随着TiC含量的增高,涂层的耐磨损性能较之基体和Fe06涂层显著升高[27]。
图 12为Fe06+Mo复合涂层的磨损形貌图。Fe06+ 0.10Mo复合涂层部分涂层脱落表现出明显的粘着磨损现象, 且表面伴有深长的犁沟, 意味着发生了剧烈的磨粒磨损,如图 12a所示。从图中可以看到,随着Mo粉质量分数增多,涂层表现出轻微的粘着磨损和磨粒磨损,涂层的片状脱落变小,细条痕变得短而浅。图 12b、图 12c所示分别为Fe06+0.15Mo和Fe06+0.20Mo复合涂层的磨损形貌,表现出良好的耐磨性能。说明随着Mo粉含量的增多,涂层的耐磨损性能显著升提升,Mo粉增强了涂层的耐磨性。相比Fe06+TiC复合涂层,Fe06+Mo复合涂层以粘着磨损为主,耐磨损性能优于Fe06+TiC复合涂层。
激光熔覆Fe06+(TiC/Mo)复合涂层硬度及耐磨性能研究
Study on hardness and wear resistance of laser cladding Fe06+(TiC/Mo) composite coatings
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摘要: 为了提高石油钻杆材料42CrMo的硬度及耐磨性能, 通过激光熔覆技术制备不同质量分数(0, 0.10, 0.15, 0.20)Fe06+TiC/Mo复合涂层。采用显微硬度仪器、扫描电镜、摩擦磨损试验机进行了显微硬度、耐磨性能、物相组成、磨损行为分析和实验验证, 得到的熔覆层主要由α-Fe、Cr-Fe以及(Fe、Ni)固溶体等相组成。结果表明, Fe06+TiC复合涂层硬度平均约1180 HV0.2, Fe06+Mo复合涂层硬度平均约893 HV0.2; Fe06+TiC复合涂层的磨损量平均约2.97 mg, Fe06熔覆层磨损量为7.8 mg, Fe06+Mo复合涂层的磨损量平均约2.67 mg; Fe06+TiC/Mo复合涂层磨损机理以粘着磨损、磨粒磨损为主, Fe06+0.2TiC熔覆层硬度最高, Fe06+0.2Mo熔覆层耐磨性能最好。该研究为提高42CrMo材料硬度及耐磨性能提供了实践参考。Abstract: In order to improve the hardness and wear resistance of oil drilling pipe material 42CrMo, Fe06+TiC/Mo composite coatings with different mass fractions (0, 0.10, 0.15, 0.20) were prepared by laser cladding technique. The microhardness, wear resistance, phase composition, wear behavior, and experimental verification were carried out by microhardness instrument, scanning electron microscope, and friction and wear testing machine. It was found that the cladding layer was mainly composed of α-Fe, Cr-Fe and (Fe, Ni) solid solution phases. The results show that the average microhardness of Fe06+TiC composite coating about 1180 HV0.2, and that of Fe06+Mo composite coating is about 893 HV0.2. The average mass loss of Fe06+TiC composite coating is about 2.97 mg, the average mass loss of Fe06 cladding layer is 7.8 mg, and the average mass loss of Fe06+Mo composite coating is about 2.67 mg, respectively. The wear mechanism of Fe06+TiC/Mo composite coating is mainly adhesion wear and abrasive wear. The hardness of Fe06+0.20TiC cladding is the highest, and the wear resistance of Fe06+0.20Mo cladding is the best. This study provides practical reference for improving the hardness and wear resistance of 42CrMo materials.
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Key words:
- laser technique /
- wear resistance /
- microhardness /
- wear behavior /
- mass loss
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表 1 基体与Fe06粉末化学成分表
Table 1. Substrate and Fe06 powder chemical composition list
compositions(mass fraction w) C Si Cr Ni B Mo Fe Fe06 0.008 0.02 0.0075 0.32 0.04 — balance 42CrMo 0.004~0.005 0.002~0.004 0.009~0.012 ≤0.003 — 0.002~0.003 — 表 2 TiC粉末化学成分表
Table 2. TiC powder chemical composition list
compositions(mass fraction w) Ti C Fe free carbon other impurity allowance TiC 0.802 0.195 0.001 0.001 0.003 表 3 磨损率
Table 3. Wear rate
samples substrate Fe06 0.10TiC 0.15TiC 0.20TiC 0.10Mo 0.15Mo 0.20Mo wear rate/(10-6mg·m-1) 16.2471 6.4656 3.0670 2.4039 1.9065 2.6526 2.2381 1.7408 -
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