【作者】 张锋刚；

【导师】 朱小鹏； 雷明凯；

【作者基本信息】 大连理工大学 ， 材料表面工程， 2013， 博士

【摘要】 以Ni代Co粘结相可提高WC基硬质合金的耐高温、耐腐蚀、防辐射等性能,但力学性能和耐磨性能有所降低,为进一步提高WC-Ni系硬质合金的耐磨性,延长硬质合金零部件在极端服役条件下的使役寿命,分别利用TEMP-6型强流脉冲离子束(HIPIB)装置和紧凑型强流脉冲电子束(HIPEB)装置上,开展了二类强流脉冲荷电粒子束辐照WC-13Ni硬质合金改性实验研究,揭示了辐照硬质合金表面形貌、表面粗糙度、相结构、表面硬度,以及摩擦学性能的变化规律,获得了具有减摩耐磨性能的改性表面,阐明了强流脉冲荷电粒子束辐照Ni粘结WC基硬质合金表面改性机制。采用能量密度1-6J/cm2,脉冲宽度70ns,辐照次数1～10次的HIPIB辐照WC-13Ni硬质合金,硬质合金表面发生熔融和Ni粘结相的选择性烧蚀,形成具有微区光滑致密化的“峰-谷”起伏特征的烧蚀重熔表面形貌,硬质合金表面粗糙化,表面粗糙度Ra随着能量密度和辐照次数显著增加,6J/cm2、10次辐照可使硬质合金R。由原始的0.13μm增加至1.62μm。辐照硬质合金表层发生六方相a-WC向立方相β-WC1-x转变,且转变量随能量密度和辐照次数增加。HIPIB辐照使WC-13Ni硬质合金表面发生硬化。单次或多次辐照硬质合金表面显微硬度均随能量密度的增加呈“先增加-后减小-再增加”的变化趋势,6J/cm2、10次辐照表面显微硬度由原始的11.84GPa提高至16.60GPa。HIPIB辐照硬质合金表层具有“长程硬化”效应,硬化层深度随能量密度和辐照次数增加,6J/cm2、10次辐照硬化层深度可达160μm。环-块式摩擦磨损实验表明,HIPIB辐照显著降低了硬质合金的表面摩擦系数和磨损率,6J/cm2、10次辐照硬质合金具有最佳的减摩耐磨性能,摩擦系数从原始的0.80减小到0.48,磨损率从原始1.2×10-6mm3/Nm减小到3.6×10-7mm3/Nm,较原始硬质合金降低约70%。采用能量密度3-34J/cm2,脉冲宽度180ns,辐照次数1～10次的HIPEB辐照WC-13Ni硬质合金,硬质合金表面发生熔化、烧蚀与喷发,快速冷凝后形成具有“火山坑”以及烧蚀孔等典型特征的起伏状重熔喷发表面形貌,硬质合金表面粗糙化。R。的变化规律与HIPIB辐照相似,较高能量密度、多次辐照的Ra增大,34J/cm2、10次辐照可使Ra由原始的0.21μm显著增加到1.26μm。辐照硬质合金表层发生六方相a-WC向立方相β-WC1-x和六方相a-W2C转变,且转变量随能量密度和辐照次数增加；在高能量密度条件下,辐照表面有石墨C形成。HIPEB辐照使WC-13Ni硬质合金表面产生不同程度的硬化与软化。3J/cm2、1次辐照表面显微硬度达到最大值,约13.70GPa,34J/cm2、5次辐照表面显微硬度降低至最小值,约10.49GPa。 HIPEB辐照表面硬化和软化的硬质合金试样均具有“长程硬化”效应,硬化层深度随能量密度和辐照次数增加,34J/cm2、10次辐照硬化层深度可达380μm。环-块式摩擦磨损实验表明,HIPEB辐照显著降低了硬质合金的表面摩擦系数和磨损率,34J/cm2、10次辐照硬质合金具有最佳的减摩耐磨性能,摩擦系数从原始的0.80减小到0.54,磨损率从原始1.2×10-6mm3/Nm减小到3.8×10-7mm3/Nm,较原始硬质合金降低约68%。HIPIB辐照的最大能量沉积在表层数百nm范围内,使硬质合金表面发生强烈的熔融与选择性烧蚀,形成“峰-谷型”起伏形貌；而HIPEB辐照的最大能量沉积于亚表层,约数μm处,造成亚表层优先熔化以及亚表层熔体的喷发,易形成火山坑形貌。二类强流脉冲荷电粒子束辐照的极速加热和冷却过程,可导致WC相中碳的反应烧损和急冷淬火,有助于β-WC1-x亚稳相形成；HIPEB脉冲作用时间较长且能量作用深度更大,相对缓慢的加热冷却过程和更长的高温反应导致较多的碳损失和部分β-WC1-x相分解促使α-W2C亚稳相和石墨C相的形成。辐照硬质合金的表面硬化归因于表面重熔致密化和Ni粘结相含量减少,而HIPEB辐照硬质合金表面α-W2C亚稳相形成对表面硬化也有贡献；β-WC1-x亚稳相的形成对HIPIB辐照硬质合金表面硬化有降低作用,而β-WC1-x亚稳相和表面烧蚀孔隙或裂纹缺陷的形成是HIPEB辐照硬质合金表面软化的原因。辐照应力波的冲击强化作用导致WC-Ni硬质合金表层位错、空位等晶体缺陷形成是硬质合金表层“长程硬化”的原因,硬化效果取决于应力波的宽度和强度,HIPEB辐照应力波宽度较大,硬化层较深,而HIPIB辐照可以在较低能量密度获得更为显著的硬化效果。原始WC-Ni硬质合金的磨损以Ni粘结相的塑性变形和WC晶粒脱落为主要特征的磨粒磨损,耐磨性依赖于硬质合金的硬度。二类强流脉冲荷电粒子束辐照硬质合金磨损机制相似,耐磨性提高不仅仅与表面硬度相关,也与辐照改性的组织特性相关。辐照引入表面熔化导致原始硬质合金中WC晶粒与Ni粘结相之间微孔缺陷愈合,在滑动摩擦磨损的初始阶段硬质合金表面熔层组织被逐渐磨削,局部区域发生片状粘着,磨损机制主要为微观切削和粘着磨损。稳定磨损阶段的磨损机制与原始硬质合金相似,但辐照冲击波在较长范围的深度硬化效应使硬质合金中WC晶粒与Ni粘结相之间的结合力增强,以及Ni粘结相自身强化有效抑制了滑动摩擦磨损过程中Ni粘结相的微观磨损和随后WC晶粒的脱落。更多还原

【Abstract】 Replacement of Co by Ni is found to improve the corrosion reistance, heat stability and anti-radiation of WC based cemented carbide, but its mechanical properties and wear resistance are lower than that of WC-Co system cemented carbide. In order to improve the wear resistance and lifetime of the WC-Ni system cemented carbide and its components under the extreme condition, the experimental investigation of the WC-13Ni cemented carbide irradiated by high-intensity pulsed charged particle beams are performed in TEMP-6type high-intensity pulsed ion beam (HIPIB) apparatus and compact high-intensity pulsed electron beam (HIPEB) apparatus, respectively. The modification mechanism of nickel cemented tungsten carbide irradiated by high-intensity pulsed charged particle beams are illustrated in terms of the change on surface morphology, phase structure, surface roughness, surface microhardness, and tribological performance of modified surface, respectively.The WC-13Ni cemented carbides were irradiated by HIPIB at energy densities of1-6J/cm2and shot number of1～10with a pulse width of70ns. The surface remelting and selective ablation of nickel binder phase resulted in the formation of a "hill-valley" surface morphology with smoothed and densified in microscale on the irradiated surfaces. The surface roughness Ra increased with increasing energy density and shot number, and Ra for irradiated sample at6J/cm with10shots significantly increased from0.13μm for original sample to1.62μm. It is found that the phase transformation from hexagonal a-WC to cubic β-WC1-x underwent in the irradiated surface layer, and the amount of β-WC1-x phase increaed with increasing energy density and shot number. Surface hardening in different degrees is observed on the HIPIB irradiated samples compared with the original samples. Surface microhardness of the irradiated samples at a fixed shot number presented a similar hardening tendency with increasing the energy densities, i.e."increase-decrease-increase", and surface microhardness of irradiated sample at6J/cm2with10shots significantly increased from11.84GPa for original sample to16.60GPa. The HIPIB irradiation led to the "long range hardening" on the surface layer of WC-13Ni samples, and the depth of hardened layer increased with increasing energy density and shot number, where the depth of hardened layer reached to160μm for the irradiated sample at6J/cm2with10shots. The block-on-ring wear test demonstrated that the friction coefficient and specific wear rate of HIPIB irradiated samples obviously decreased. The HIPIB irradiated samples at6J/cm2with10shots exhibited the superior tribological performance, the friction coefficient decreased from0.80for the original sample to0.48. Correspondingly, the specific wear rate decreased from1.2×10-6mm3/Nm to3.6×10-7mm3/Nm, which is approximately reduced by70%compared with that of the original sample.The WC-13Ni cemented carbides were irradiated by HIPEB at energy densities of3～34J/cm2and shot number of1-10with a pulse width of180ns. The surface remelting, ablation and ejection, as followed by fast re-solidification resulted in a typical ablated-ejected surface topography with some craters and blow holes formed on the irradiated surfaces. Similar to the HIPIB irradiation, the higher energy density and multiple shots,Ra increased more remarkably, and Ra significantly increased from0.21μm for original sample to1.26μm for irradiated sample at34J/cm2with10shots. It is found that the phase transformation from hexagonal a-WC to cubic β-WC1-x and hexagonal a-W2C underwent in the irradiated surface layer, and the amount of β-WC1-x, phase increased with increasing energy density and shot number. Moreover, the graphite C phase can also be observed on the surface of irradiated sample at the higher energy density of34J/cm2. Surface hardening and softening in different degrees was observed on the HIPEB irradiated samples compared with the original samples. The surface microhardness of irradiated samples reach to a maximal value of13.70GPa at3J/cm2with1shot, and reach to a minimal value of10.49GPa at34J/cm2with5shots. The "long range hardening" phenomenon is observed on all the HIPEB irradiated WC-13Ni samples with surface hardening and softening, and the depth of the hardened layer increased with increasing energy density and shot number, where the depth of hardened layer reached to380μm for the irradiated sample at34J/cm2with10shots. The block-on-ring wear test demonstrated that the friction coefficient and specific wear rate of HIPEB irradiated samples obviously decreased. The HIPEB irradiated samples at34J/cm2with10shots exhibited the superior tribological performance, the friction coefficient decreased from0.80for the original sample to0.54. Correspondingly, the specific wear rate decreased from1.2X10-6mm3/Nm to3.8×10-7mm3/Nm, which is approximately reduced by68%compared with that of the original sample.The maximum energy of HIPIB irradiation deposited in the several hundreds nm range of the surface layer of WC-13Ni samples, and led to more stronger surface melting and ablation to form a "hill-valley" surface morphology. However, the maximum energy of HIPEB irradiation deposited in the subsurface layer of WC-13Ni samples, about several μm, and led to the subsurface layer melting and melt eruption to form the craters. High-intensity pulsed charged particle beams irradiation with rapid heating and cooling led to carbon loss of WC in short pulse and rapid quenching, and contributed to the formation of metastable β-WC1-x phase. Moreover, HIPEB irradiation have longer pulse action time and larger energy deposited range than HIPIB irradiation led to slower heating and cooling rate and longer high-temperature reaction, and contributed to much more carbon loss of WC and decomposition of some β-WC1-x phases to form metastable a-W2C phase and graphite C phase. Surface hardening of the irradiated samples is resulted from the decreasing of the nickel binder phase content and densification in the surface layer, and the formation of a-W2C phase on the surface layer of HIPEB irradiated samples also increased hardening effect. The formation of metastable β-WC1-x phase only reduced the surface hardening degree of HIPIB irradiated samples, but the reason of surface softening of HIPIB irradiated samples is the formation of β-WC1-x phase and some defects, such as cracks and blow holes and so on. The reason of the "long range hardening" on the surface layer of the irradiated samples is the formation of crystal defects, such as dislocation, vacancy and so on, which is resulted from the impact action of the stress wave by high intensity pulsed charged particle beams irradiation. Hardening effect depends on the width and intensity of stress wave. HIPEB irradiation have deeper hardening layer than HIPIB irradiation because it have longer width of stress wave, but an more significant hardening effect is achieved for HIPIB irradiated samples at lower energy density. The wear mechanism of original WC-Ni cemented carbide during the wear process is abrasive wear with the main characteristics of plastic deformation of Ni binder phase and fall-out of WC grains, and wear resistance depends on the hardness of cemented carbide. The irradiated samples by both high-intensity pulsed charged particle beams have similar wear mechanism, and the improved wear resistance of irradiated samples is not only related to surface hardness, but also associated with the features of modified structure. Irradiation led to surface healing of original defects of micro-pores between WC grains and binder phase by surface remelting. At the initial stage of sliding wear process, the melted layer was gradually worn out and some regions smeared flack-shape debris, and the main mechanisms of the irradiated samples are micro-abrasion and adhesive wear. In the steady-state stage of sliding wear, the wear mechanism of the irradiated samples is similar to that of original sample, but the micro-abrasion of Ni binder phase and subsequent pull-out of WC grains can be effectively restricted in the irradiated samples during the sliding wear process, as result of bonding force between WC grains and Ni binder phase, and strengthening of binder phase itself by the hardened effect in the long range from shock waves of beams irradiation.更多还原