【作者】 颜培；

【导师】 邓建新；

【作者基本信息】 山东大学 ， 机械制造及其自动化， 2012， 博士

【摘要】 本文采用脉冲偏压辅助沉积多弧离子镀与离子轰击相结合的工艺制备了以硬质合金为基体的ZrTiN梯度涂层刀具,并对其设计理论、涂层结构、涂层工艺、性能、微观结构、摩擦磨损性能及切削性能进行了系统深入的研究。对三元氮化物TiAlN、ZrTiN和TiCrN的固溶强化机制进行分析,并采用物质吉布斯自由能函数法,分析计算ZrTiN涂层、基体及过渡层各组分间的化学反应,结果表明：ZrTiN涂层是以ZrN为基础相的稳定固溶体；涂层与基体不发生化学反应,而Ti过渡层与基体的化学反应能够在膜-基界面形成以化合物结合的界面。对ZrTiN涂层与基体材料的物理相容性进行了研究,详细分析了涂层残余热应力分布规律,结果表明YT15基体与ZrTiN涂层的匹配性较好；涂层残余热应力随温度的升高而增大,随涂层厚度的增加而减小；TiZr过渡层的加入可以有效减小界面处的残余热应力,尤其是剪应力。基于膜-基界面结合类型以及涂层附着机理,分析了涂层结合力的影响因素；以提高结合力为目标,设计出四种不同结构的ZrTiN涂层：单层ZrTiN涂层(SZT),带有成分梯度过渡层的涂层(TGC),热膨胀系数梯度分布的涂层(EGC)以及结合力-硬度梯度分布的涂层(ZGC)。采用脉冲偏压辅助沉积多弧离子镀与离子轰击相结合的工艺,在硬质合金基体上进行ZrTiN涂层,全面系统地研究了靶电流、氮气流量、沉积温度、沉积时间、基体负偏压等沉积参数对涂层微观结构及性能的影响规律。结果表明,靶电流对涂层中Zr/Ti的原子百分比及晶胞参数影响明显；氮气流量增大或沉积温度升高均会导致ZrTiN晶体的择优取向从(111)变为(200),并伴随着晶粒尺寸的增大；基体负偏压对涂层晶粒取向影响最明显：基体负偏压升高,ZrTiN晶体的择优取向从(111)变为(200),最终变为(220),同时涂层表面质量明显下降。YT15基体上的ZrTiN涂层结构致密,元素分布均匀,界面结合紧密,其性能明显优于YG8基体上的涂层。YT15基体上的ZrTiN涂层的最佳沉积参数为：基体负偏压250V；Zr靶电流110A,Ti靶电流70A；氮气流量140seem:沉积时间60-90min之间；沉积温度200℃。以YT15为基体,制备出SZT、TGC、EGC(?)ZGC四种ZrTiN涂层刀具,并分析其性能及微观结构。SZT涂层刀具的硬度最高,为32.6GPa; EGC涂层刀具的结合力最大,为84.6N；四种涂层的厚度在2.62-2.73μm之间；涂层晶体结构均呈(111)择优取向；涂层元素向基体发生较为明显的扩散,基体向涂层的扩散比较轻微；涂层与基体的界面结合为机械啮合、元素扩散和形成化合物的形式共存。系统研究了ZrTiN涂层的摩擦磨损特性,结果表明：ZrTiN涂层与淬火40Cr的摩擦系数及磨损率均随Zr与Ti原子比的增大而减小,N元素含量对摩擦磨损性能影响不明显。载荷增加,涂层的摩擦系数增大而磨损率减小；滑动速度增大,摩擦系数和磨损率均减小。轻载时ZrTiN涂层的磨损形式是轻微的磨粒磨损及剥落,表面硬度高的SZT、ZGC涂层耐磨性较优；重载时涂层的磨损形式是磨粒磨损、脆性断裂及剥落,韧性较好、层-基结合力较高的TGC、EGC涂层耐磨性能较优。低速下涂层的磨损形式是工件粘结及涂层剥落,韧性及结合力较好的TGC、EGC涂层耐磨性能较优；高速下涂层的磨损形式是轻微的磨粒磨损,EGC涂层的热胀系数梯度分布结构使其热应力较小,热损伤轻微,磨损率最低。对制备的ZrTiN涂层刀具以及YT15传统刀具进行干切削40Cr淬火钢的对比试验。结果表明：ZrTiN涂层刀具对切削力的影响较小,但可以显著降低切削温度,尤其是高速时ZrTiN涂层的热障作用明显。切削距离3600m时,使用涂层刀具已加工表面粗糙度明显低于YT15,表面粗糙度一致性较好。后刀面磨损为磨粒磨损、边界磨损的形式；ZGC涂层表层硬度最高、结合力较大,其多层结构可以有效抑制裂纹的扩展,后刀面磨损量最小；后刀面磨损量由小到大依次为：ZGC<EGC <TGC<SZT<YT15。前刀面磨损为月牙洼磨损、粘结磨损的形式；EGC涂层热膨胀系数的梯度分布可以有效降低热应力及热损伤,月牙洼磨损最轻微；月牙洼磨损区的面积由小到大依次为：EGC<ZGC<TGC<SZT<YT15。裂纹萌生、扩展导致的崩碎、剥落是ZrTiN涂层失效的主要原因；ZrTiN梯度涂层对裂纹的扩展起到阻断、偏转的作用,可以有效提高涂层的寿命。更多还原

【Abstract】 ZrTiN gradient coated tools were developed on cemented carbide substrates by pulsed bias assisted deposition of multi arc ion plating combined with ion beam assisted deposition technique. Friction and wear behavior, cutting performance and wear mechanism were proceed to the further and systematic research, as well as the design theory, gradient structure, deposition parameters, mechanical properties and micro-structures of the coatings.Solid solution strengthening mechanism of ternary nitride like TiAlN, ZrTiN and TiCrN were analyzed. Chemical reactions among ZrTiN coating, cemented carbide substrate and metal adhesion layer were analyzed and calculated by Gibbs free energy change of reaction. The results show that ZrTiN is a stable solid solution based on ZrN; there is no chemical reaction between coating and substrate; chemical reaction of Ti adhesion layer and substrate forms the combination of compounds at the interface. Physical compatibility of ZrTiN coating and substrate are investigated, and the distribution of thermal residual stress of coating is analyzed detailedly. The results indicate that the optimum substrate material matched with ZrTiN coating is YT15; thermal residual stress of the coating increases with increasing depositing temperature, while decreases with increasing coating thickness; TiZr adhesion layer can effectively reduce the thermal residual stress, especially shear stress.Based on the type of coating-substrate interface and adhesion mechanism, the factors affecting adhesive strength were analyzed. In order to improve the binding strength, different structures of ZrTiN coatings are designed:single layer ZrTiN coating (SZT); composition gradient adhesion layer coating (TGC); coating with gradient distribution of the coefficient of thermal expansion (EGC); coating with gradient distribution of adhesive strength&hardness (ZGC). ZrTiN coatings were deposited on cemented carbide substrates by pulsed bias assisted deposition of multi arc ion plating combined with ion beam assisted deposition technique. During the depositing, the basic parameters were target current, nitrogen flow rate, deposition temperature, deposition time and negative bias voltage. The effects and laws of these parameters on microscopic structures and properties of the coatings were investigated systematically. The results reveal:the target current shows obvious impact on the atomic percent of Zr/Ti and crystallographic lattice constant of ZrTiN coatings; the nitrogen flow rate increases or the deposition temperature raises will lead to the preferred orientation of ZrTiN changing from (111) to (200), accompanied with the increase of grain sizes; the negative bias voltage shows the most obvious impact on the preferred orientation of ZrTiN:as the negative bias voltage increases, the preferred orientation of ZrTiN changes from (111) to (200), ultimately (220), at the same time, the quality of the coating surface decreases. The film on YT15substrate exhibits a dense and fine grained structure with the elements distributing quite evenly, and the combination of film and substrate is compact. The properties of the films on YT15substrate are much better than YG8substrate. The suitable deposition parameters for coating on YT15substrate are:negative bias voltage250V, Zr target current110A, Ti target current70A, nitrogen flow rate140seem, deposition time60-90min, deposition temperature200℃。Based on YT15cemented carbides, SZT, TGC, EGC and ZGC coated tools were prepared, and then properties and microstructures of these four kinds of coated tools were analyzed. The results indicate that SZT coated tools show the highest surface hardness of32.6GPa, and EGC coated tools with the highest adhesive strength of84.6N; the coating thickness is among2.62-2.73μm; all the crystal structures of the four show (111) preferred orientation. The element diffusion of the coating to the substrate is obvious, while the element diffusion of the substrate to the coating is relatively slight; the interfacial bonding of ZrTiN and YT15substrate is combining effect of mechanical toothing, element diffusion and formation of compounds. A further research which regarded to the friction and wear behavior of the ZrTiN coatings displays that both the friction coefficient and the wear rate of ZrTiN coatings against40Cr hardened steel decrease with the increase of atomic ratio of Zr:Ti, and the influence of N element content is not distinct. If the applied load increases, the friction coefficient of the coating increases while the wear rate decreases; if the sliding speed increases, both the friction coefficient and the wear rate decrease. When at a low applied loads of friction, the form of the wear mechanism of the coatings performs a mild abrasive wear and flake, at the same time SZT and EGC coatings with high surface hardness show better wear resistance; when at a heavy applied loads of friction, the wear mechanism displays a state of abrasive wear, and the form of this performs brittle fracture and flake, meanwhile TGC and EGC coatings with better toughness and adhesive strength show better wear resistance. The form of wear mechanism of the coatings at low sliding speed performs adhesive wear and brittle fracture, moreover TGC and EGC coatings with higher toughness and adhesive strength show better wear resistance; the wear mechanism is mild abrasive wear at high sliding speed, and EGC coating with the gradient distribution of the coefficient of thermal expansion shows the best wear resistance, as the thermal stress of the coating is small and the thermal injury is mild.Experiments which used the ZrTiN coated tools of dry cutting of40Cr hardened steel were carried out, compared with YT15tools. The results indicate that the effect of ZrTiN coated tool on cutting force is not obvious, while the coating can significantly reduce the cutting temperature; the thermal barrier effect of ZrTiN coating is obvious, especially in high speed cutting. When the cutting distance is3600m, the machined surface roughness of coated tools is significantly lower than YT15, while the machined surface roughness has more consistencies. Flank wear of the tool is the form of abrasive wear and boundary wear; ZGC coating has high surface hardness and adhesive strength, and the multilayer structure can effectively suppress the crack diffusion, so the amount of flank wear is the smallest. The order of ascending the flank wear is ZGC<EGC< TGC<SZT<YT15. Rake wear of the tool is the form of crater wear and adhesive wear; EGC coating with the gradient distribution of the coefficient of thermal expansion can effectively reduce the thermal stress and the thermal injury of the coating, and the crater wear is the slightest. The order of ascending the crater wear zone area is EGC<ZGC<TGC<SZT<YT15. The main reasons for the failure of ZrTiN coating are brittle fracture and flake caused by the initiation and propagation of the crack; ZrTiN gradient coatings play an important role in blocking and deflecting the cracks, moreover they can effectively improve the life of the coating.更多还原