微织构参数变化对硬质合金摩擦特性的影响

采用金刚石压头划痕法在抛光后的硬质合金表面制备了平行微织构,划痕载荷分别为5,10,15 N,织构间距为30,50,80,100μm。在UTM-2摩擦磨损试验机上进行了微织构硬质合金的摩擦磨损试验,对摩擦因数进行了在线测量,并利用超景深显微镜观察了表面微织构摩擦磨损形貌。试验结果表明:硬质合金的表面微织构有助于降低摩擦因数,当划痕载荷为10 N、织构间距为30μm时,摩擦因数最小,只有0.36。     

齿轮钢和蓝宝石的低速摩擦特性对比研究

通过单颗磨粒划擦试验,研究齿轮钢(42Cr Mo V)和蓝宝石(α-Al2O3)的摩擦磨损特性。采集划擦试验过程中的力信号,比较在不同的划痕深度、划痕速度和压头角度条件下,齿轮钢和蓝宝石分别与金刚石压头所形成的摩擦副的摩擦因数μ。结果表明:划痕深度、划痕速度对两种材料与金刚石压头所形成的摩擦副的摩擦因数μ均无影响;压头角度对两种材料与金刚石压头所形成的摩擦副的摩擦因数μ均有影响,且随着压头角度的增大,两种材料与金刚石压头所形成的摩擦副的摩擦因数μ均增大;在相同试验条件下,蓝宝石与金刚石压头所形成的摩擦副的摩擦因数大于齿轮钢与金刚石压头所形成的摩擦副的摩擦因数。     

ZrN涂层刀具的滑动磨损特性研究

山东大学摘要:采用电弧离子镀法在硬质合金刀具表面制备了厚度为2.19~5.23μm的ZrN系列涂层,测定了涂层的显微硬度,并通过划痕试验和摩擦磨损试验考察了涂层与基体的结合强度及其摩擦磨损性能。在扫描电镜下观察磨损表面形貌,结果表明:ZrN系列涂层能够显著提高硬质合金刀具的表面硬度;涂层与基体的结合强度较高,划痕临界载荷高于60N;与此同时,电弧离子镀法ZrN系列涂层可以显著改善硬质合金刀具的耐磨性能。磨损机理主要是磨粒磨损和涂层的微剥落。     

织构参数对不锈钢与猪股骨间摩擦性能的影响

采用YLP-F20激光打标机在4Cr13不锈钢圆盘试件表面加工出不同尺寸的沟槽微织构试样;将织构试样与新鲜猪股骨制成的骨棒试样构成销-盘摩擦副,在立式万能摩擦磨损试验机上进行摩擦磨损试验,研究微织构参数对不锈钢与猪股骨在生理盐水润滑下的摩擦特性的影响。结果表明:沟槽型的摩擦因数比无沟槽的要小,在文中研究的范围内摩擦因数随着沟槽宽度的增加而减小,随着沟槽间角度的增加而增加;对加工微织构后的表面进行处理对摩擦因数的影响很大。文中研究范围内宽度200μm、深度20μm、角度1.21°微织构组合,相比较于无微织构试件摩擦因数最大降低了36.4%。     

金刚石涂层微铣刀的铣削加工试验

为了掌握金刚石涂层对其铣削性能的影响,针对直径为50 μm级的硬质合金微铣刀,进行了金刚石涂层与未涂层硬质合金微铣刀具微槽铣削试验。通过使用线电极电火花磨削技术制备出直径为50 μm级的D形微铣刀,采用金刚石涂层和未涂层刀具在纯铜工件上开展微槽铣削工艺试验;使用白光干涉仪、超景深显微镜等仪器来观测微槽表面形貌、粗糙度等随铣削距离变化的规律,分析金刚石涂层对硬质合金微铣刀铣削加工质量的影响。结果表明：采用金刚石涂层刀具加工的微槽具有较少的毛刺,表面粗糙度值约为未涂层刀具铣削的粗糙度值的1/2,并且能够在一定距离内保持稳定的槽宽、粗糙度值和侧面形貌。     

表面微织构影响点接触润滑摩擦性能的实验研究

针对球-盘高副点接触开展微织构表面摩擦学性能实验研究。采用激光工艺在试样表面上加工出具有一定形状、深度和面积比的矩形微织构,采用三维表面形貌仪测量微织构的形貌特征,在摩擦磨损实验机上进行摩擦学实验,研究往复运动模式下微织构深度、间距等参数对球-盘点接触润滑摩擦性能的影响。结果表明:较浅的微织构具有相对较小的摩擦因数;较高频率下微织构表现出较好的润滑和减摩效果;沿运动方向的微织构间距增大,摩擦因数逐渐降低,超过Hertz接触直径之后,摩擦因数变化不明显;垂直于运动方向微织构边长增大,摩擦因数呈现先减小后增大的变化趋势。     

硬质合金表面正弦微织构对其摩擦磨损性能的影响研究

为了探讨微织构对硬质合金表面摩擦磨损性能的影响,利用激光技术在硬质合金表面制备了一种正弦状沟槽型微织构,并在UMT-2摩擦磨损试验机上进行直线往复式摩擦磨损试验。试验分别在不同载荷、滑动速度和润滑条件下,对微织构化硬质合金表面的摩擦磨损性能进行评价。研究表明:硬质合金表面加工微织构并添加固体润滑脂能够有效降低硬质合金表面的摩擦系数;在同等条件下,正弦型微沟槽表面比传统直线型微沟槽表面具有更好的减磨性能;在高载荷和高滑动速度并添加润滑脂的条件下,正弦型微织构试样表面的减磨性能最好。     

激光微织构表面脂润滑性能试验研究

采用声光调 Q 二极管泵浦固体光源（DPSS）Nd∶YAG 激光器,在45＃钢试样表面进行激光微织构加工,采用 VYKO-NT1100三维形貌分析仪对微观织构形貌进行测量。以二硫化钼润滑脂为润滑剂,在 MMW-1A 型摩擦磨损试验机上进行微织构试样和光滑试样在不同工况条件下的摩擦性能对比试验。试验结果表明,在一定条件下,面积占有率为14％的微凹腔织构表面的脂润滑性能明显优于未织构光滑表面,且随着微凹腔面积占有率的增大,摩擦因数波动范围变小;凹槽织构表面较未织构光滑表面具有更好的润滑稳定性;在脂润滑条件下,激光微织构表面较未织构光滑表面摩擦因数最大可降低26％。     

组合型微织构化铝合金表面的摩擦学性能研究

为改善铝合金的摩擦学性能,运用有限元方法对单一方形凹坑、条形凹槽、方形凹坑和条形凹槽组合3种不同形貌织构摩擦副间润滑油膜承载能力进行仿真分析,并探究不同织构尺寸对油膜承载能力的影响。仿真结果表明：方形凹坑和条形凹槽组合织构润滑油膜承载能力最佳。采用脉冲Nd:YAG激光器在铝合金试件表面加工出具有规则形貌的方形凹坑和条形凹槽组合的织构阵列,借助CFT-I型高速往复摩擦磨损试验机进行摩擦试验,研究织构几何尺寸对摩擦副接触面间摩擦学性能的影响规律,并利用超景深显微系统对试件磨损表面的形貌进行观测。试验结果表明：组合织构化表面的平均摩擦因数与无织构表面相比明显减小,且波动幅度较小;当织构尺寸为80μm时,织构表面的摩擦因数最小,且试验得到的基体表面磨痕深度随织构尺寸的变化规律,与仿真计算得到的润滑油膜升力系数的变化规律相吻合,为微织构参数设计提供了一定的理论依据。     

纳米流体与微织构耦合作用对刀具材料摩擦磨损性能的影响研究

合理的表面织构可有效改善摩擦副界面间的摩擦状态。为研究纳米流体与表面微织构耦合作用对硬质合金刀具材料摩擦性能的影响,采用“两步法”将纳米Fe3O4颗粒添加到水基切削液基础液,制备出质量分数为0.5%的Fe3O4纳米流体,并利用激光微加工技术在光滑的YG6X硬质合金样件表面制备出不同尺寸参数的沟槽型与凹坑型表面微织构。分析纳米流体与表面微织构耦合作用下硬质合金样件的摩擦磨损性能,整理摩擦系数、样件表面磨损形貌、磨球磨损率等数据发现,纳米流体能够有效改善基础液的润滑性能,在一定尺寸形状的织构样件相互作用下表现出优异的抗磨减摩性能,并且揭示了相应的减摩抗磨机理。     

微织构(W,Mo)C基刀具和YG8刀具对钛合金干切削性能的影响

刀具切削钛合金时存在切削温度高、单位面积上切削力大等问题,微织构刀具可以有效减小摩擦力,减小切削力。通过正交实验法设计微织构参数,研究微织构参数对Al 2O 3/La 2O 3/(W,Mo)C无黏结相硬质合金刀具以及YG8刀具切削钛合金实验的切削性能影响。实验结果表明,合适参数的沟槽型微织构能有效降低Al 2O 3/La 2O 3/(W,Mo)C无黏结相硬质合金刀具和YG8刀具切削TC4钛合金的切削力,相同沟槽参数下,无黏结相硬质合金刀具的切削力明显低于YG8刀具的切削力;合适参数的沟槽型微织构能有效降低刀具刀屑界面的摩擦系数,相同沟槽参数下,无黏结相硬质合金刀具的摩擦系数大都低于YG8刀具的摩擦系数;沟槽深度10μm、沟槽间距100μm以及沟槽宽度30μm的沟槽参数下,切削钛合金时,无黏结相硬质合金刀具前刀面无明显磨损,后刀面只有边界磨损,YG8刀具发生崩刃,前刀面出现切屑的滞留。     

Study on effects of tip geometry on AFM nanoscratching tests

To investigate effects of tip geometry on AFM nanoscratching process, an experimental calibration method measuring three-dimensional (3D) scratching forces based on the cantilever deflection is presented. On the surface of single crystal copper and silicon, nanoscratching tests are carried out using a pyramidal diamond tip. Effects of tip geometry (including the hemisphere of the tip and three sides of the pyramid) on scratching forces, friction coefficient and specific energy are studied. Results show that the scratching depth of about 10–15 nm is a transition point in scratching tests for the diamond tip used in this paper. Below this value, the hemisphere is dominant, whereas at the scratching depth of larger than this value, three sides of the tip play the key role in scratching tests. Friction coefficients are different at different tip orientations influenced by the contact area between the tip and the sample and attack angle at the scratching depth of greater than 10–15 nm. Specific energy is not sensitive to tip geometry because it reveals the energy required for removal of materials.     

Adhesion and friction studies of a nano-textured surface produced by spin coating of colloidal silica nanoparticle solution

This paper presents the results of adhesion and friction studies on a nano-textured surface. The nano-textures were produced by spin coating colloidal silica nanoparticle solution on a flat silicon substrate. Surface morphology was characterized by environmental scanning electron microscopy (ESEM) and scanning probe microscopy (SPM). Adhesion and friction studies were conducted using a TriboIndenter employing diamond tips with 5 μm and 100 μm nominal radii of curvature. The results show that the adhesion forces and coefficients of friction of the nano-textured surface measured by the 100 μm tip were reduced up to 98 and 88%, respectively, compared to those of a baseline silicon oxide film surface.     

Experimental assessment of textured tools with nano-lubricants in orthogonal cutting of titanium alloy

In this study, we investigated the effects of composite nano-Cu/WS₂ lubricating oil and single-point diamond indentation-textures on improving the cutting performance of YG8 cemented carbide tools, which is crucial for textures tool applications. The aims of the study were to improve wear resistance and reduce chip adhesion at the tool’s rake face in cutting of titanium alloys. Dot textures with different spacings were fabricated on the surface of YG8 cemented carbide tools through the single-point diamond indentation method, and composite nano-Cu/WS₂ lubricating oil was prepared. Orthogonal cutting tests were carried out under dry cutting and minimal quantity lubricated (MQL) conditions. Investigate the effect of different texture spacing on the cutting performance in the light of cutting forces, friction coefficient, the deformed chip thickness, tool adhesions, and chip morphology. The results show that the dot texture effectively improved the lubrication conditions in machining titanium alloys under the MQL conditions. The dot texture is effective at low speed in the dry cutting conditions. With the increase of cutting speed, the friction coefficient of dot texture tool is affected by texture spacing, and the friction coefficient of DT-200 tool is the smallest. In addition, composite nano Cu/WS₂ lubricating oil forms a lubricating film on the wear path by atomizing the lubricating oil and stores it in the dot texture, which enhances the anti-wear performance in the cutting process and reduces the cutting force and friction coefficient at the tool chip interface. By evaluating cutting force, friction coefficient, chip and tool morphology, it is concluded that DT-100 tool is more effective in improving lubrication conditions.

     

硬质合金基体预处理工艺对CVD金刚石涂层附着性能的影响

采用热丝CVD法通过不同基体处理工艺在YG8和YG6硬质合金基体上沉积了金刚石涂层,考察了基体表面预处理工艺对基体表面形貌、残留钴含量以及涂层结合力的影响。实验结果表明,一步法酸刻蚀的最佳作用时间为15min左右,无论采用一步法还是二步法,处理后的YG8硬质合金基体表面残留钴均已大幅降低至3%左右,而二步法处理后YG6基体表面钴含量仅为0.66%。通过压痕实验对比分析得出,一步法酸处理15min后的硬质合金基体上沉积的金刚石涂层压痕较小,其最大压痕尺寸为145μm,两步法处理硬质合金基体金刚石涂层压痕面积最小,表现出良好的附着性能。     

Ni nanodot-patterned surfaces for adhesion and friction reduction

Surface nano-patterning with Ni nanodot arrays was investigated for adhesion and friction reduction of contacting interfaces. Self-assembled anodized aluminum oxide (AAO) templates in conjunction with thermal evaporation was used to fabricate nano-patterned surfaces with ordered Ni nanodot arrays on Si substrates. Surface morphology of the Ni nanodot-patterned surfaces (NDPSs) was characterized by scanning electron microscopy (SEM). Adhesion and friction studies on a Ni NDPS and a baseline smooth Si(100) surface were conducted using a TriboIndenter employing a diamond tip with 100 μm nominal radius of curvature. The results show that the ordered Ni nanodot-patterning reduced the adhesion forces and coefficients of friction up to 92 and 83%, respectively, compared to those of the smooth silicon surface. Surprisingly, the nanoscale multi-asperity contact between the diamond tip and inhomogeneous Ni NDPSs under low loads follows a continuum contact mechanics model.     

Efficient microspark erosion-assisted machining of a monocrystalline microdiamond stylus using a heat-avoidance path

Monocrystalline diamond possesses covalent bonding making diamond extremely hard and difficult to machine. In this study, a microdiamond stylus typically used in measuring surface roughness is machined to exemplify the proposed ‘microspark erosion-assisted machining with heat-avoidance path’ technique. Based on the high thermal conductivity and weak electrical conductivity of boron-doped monocrystalline diamond, high-frequency pulsed discharge plasma is employed to efficiently perform microspark erosion machining on an extremely hard monocrystalline diamond blank. It was found that the pulse-on time and servo voltage respectively affect erosion plasma length and the erosion gap during diamond machining. Also, the safety distance and safety height of the erosion path dominate heat transfer to filler metal. These factors all affect the firmness of the brazed diamond blank on the substrate. Three mechanisms for removing carbon atoms from the diamond blank surface were observed. They are vaporization, melting, and graphitization of carbon atoms. This graphitized carbon atoms have weak electrical conductivity, which is conducive to inducing the wire-electrode to generate a greater electric field and secondary discharging, facilitating removal of additional carbon atoms. Experimental results indicate that a microdiamond stylus prototype with a tip of 10 μm can be safely formed using a ‘microspark erosion-assisted machining with heat-avoidance path’ technique, creating 93.7% repeatability of the minimum residual stylus diameter. The tangential micro-grinding facilitates the stylus tip to receive grinding from the grinding wheel's maximum tangential speed and create the precision microdiamond stylus with 1 μm in tip-radius. The applied microspark erosion-assisted machining had a diamond material removal rate that was 54% more efficient than conventional grinding of a commercial microdiamond stylus. The formed microdiamond stylus was inspected by Raman spectroscopy and verified by the surface roughness standard gauge to be up to industry standards.     

Nanotribology of a Silica Nanoparticle-Textured Surface

Tribological properties of a silica nanoparticle-textured (SNPT) surface were investigated at the nanoscale using a nanoindenter. The sample was fabricated by spin coating chemically synthesized silica nanoparticle solution onto a silicon substrate and then annealing the substrate in an N₂ environment. Environmental scanning electron microscopy (ESEM) and scanning probe microscopy (SPM) were used to characterize the morphology of the SNPT surface. Adhesion and friction experiments were performed with a diamond tip of nominal radius of curvature of 5 μ m, under contact forces of 750-1500 μ N, and with sliding speed of 0.1-2 μ m/s. The nanotribological properties of the SNPT sample were compared to those of a smooth silicon oxide film (SOF)-coated sample. The adhesion performance of the SNPT surface was found to be much better than that of the SOF surface. The coefficient of friction (COF) reduced up to 26%.

     

Nano-wear of the diamond AFM probing tip under scratching of silicon, studied by AFM

In order to improve such a widely used microtribological testing procedure as surface scratching by an AFM diamond tip, an experimental study has been carried out using single-crystalline silicon as the tested material. Wear of the AFM diamond tip under scratching was observed by a decrease in the scratch depth with increasing wear cycles and by the direct imaging of the diamond tip shape using a Si₃N₄ AFM tip. It was shown that the current widely used experimental method, which assumes the diamond tip to be non-wearable, introduces uncontrollable error into the obtained values for the tested material's wear rate. The harder the tested material, the larger may be the tip wear, and, therefore, the bigger may be its effect on the obtained wear rate values. The specific wear rates for the diamond tip and a silicon wafer were estimated to be 1.4 × 10^-9 and 4.5 × 10^-4 mm³/(N m), respectively.     

Micro-scratch evaluation of rock types—a means to comprehend rock drill wear

Drilling, transportation and handling of rock always result in wear of the equipment that comes into contact with the rock and rock fragments. Rock is normally considered rather hard, and the contact leads to abrasion, erosion and point fatigue. However, the wear mechanisms of the tools are often complex and vary in character depending on the rock type.To understand the wear mechanisms of the cemented carbide used in rock drill bits, it is central to understand how different rock types respond to severe scratching from hard tips. A cemented carbide tip with radius 10 μm was used in a scratch tester at progressive loads of 0 to 20 N and at constant loads of 10 N. The tested rock types were calcite, two types of magnetite, hematite, leptite, mica schist, granite, sandstone and quartz spanning average hardness values from 190 up to 1220 HV. The scratches were investigated in SEM and the friction coefficient between rock and the tip was measured. In addition, the wear volume of the cemented carbide tip is measured.The rock types differed significantly with respect to damage mechanism and critical load for transition from a mild to a more severe damage. The friction behaviour correspondingly shifted from rather smooth to very fluctuant. The wear of the tip was found to be correlated to the hardness of the rocks, but was also influenced by the grain size, the quartz content and isotropy. The implications from the present results on full-scale rock drill wear are discussed.