旋转超声磨削Si3 N4陶瓷用金刚石磨具磨损行为研究

热压烧结Si₃N₄陶瓷材料常应用于航天飞行器中关键耐高温零部件,但由于高硬度和低断裂韧性,其加工效率和加工表面质量难以满足制造需求。为了提高热压烧结Si₃N₄陶瓷旋转超声磨削加工质量,减小由于金刚石磨具磨损带来的加工误差,开展了磨具磨损行为研究。基于热压烧结Si₃N₄陶瓷旋转超声磨削加工实验,分析了金刚石磨具磨损形式;基于回归分析建立了金刚石磨具磨损量数学模型,揭示了加工参数及磨具参数与金刚石磨具磨损量间映射关系;并研究了磨损形式与磨具磨损量及加工表面粗糙度影响规律。结果表明：磨粒磨耗是旋转超声磨削Si₃N₄陶瓷用金刚石磨具最主要磨损形式,比例超过50%;主轴转速和磨粒粒度对磨具磨损量影响最为显著;且磨损量较小时,加工表面粗糙度值反而增加。以上研究可为提高旋转超声磨削Si₃N₄陶瓷加工精度和加工质量提供指导。     

Effect of deep cryogenic treatment on the microstructure and wear performance of Cr–Mn–Cu white cast iron grinding media

The phase transformation and grinding wear behavior of Cr–Mn–Cu white cast irons subjected to destabilization treatment followed by air cooling or deep cryogenic treatment were studied as a part of the development program of substitute alloys for existing costly wear resistant alloys. The microstructural evolution during heat treatment and the consequent improvement in grinding wear performance were evaluated with optical and scanning electron microscopy, X-ray diffraction analysis, bulk hardness, impact toughness and corrosion rate measurements, laboratory ball mill grinding wear test etc. The deep cryogenic treatment has a significant effect in minimizing the retained austenite content and converts it to martensite embedded with fine M₇C₃ alloy carbides. The cumulative wear losses in cryotreated alloys are lesser than those with conventionally destabilized alloys followed by air cooling both in wet and dry grinding conditions. The cryotreated Cr–Mn–Cu irons exhibit comparable wear performance to high chromium irons.     

Si3N4和52100钢对磨副材料对CrN薄膜干摩擦学行为的影响

利用阴极电弧离子镀技术在316L不锈钢基体上制备了CrN薄膜。采用扫描电子显微镜(SEM)、X射线衍射仪(XRD)、纳米压痕仪对CrN薄膜的形貌、成分和力学性能进行了表征。为了研究Si_3N_4和52100钢对磨副材料对CrN薄膜和316L不锈钢干摩擦行为的影响,在2N、5N、8N三种载荷下,将CrN薄膜和316L不锈钢基体与Si_3N_4陶瓷球和52100钢球分别进行了往复式滑动干摩擦实验。采用扫描电子显微镜观察了磨痕的微观形貌,并对CrN薄膜和316L不锈钢基体的磨损机制进行了分析。结果表明:CrN薄膜表面平整,缺陷较少;CrN薄膜的纳米硬度约为28GPa,弹性模量约为350GPa;与Si_3N_4陶瓷球相比,CrN薄膜与52100钢球摩擦时摩擦因数相对较小(保持在0.7左右)且更加稳定;316L不锈钢的摩擦因数远大于CrN薄膜且波动较大;对磨球为Si_3N_4陶瓷球时,CrN薄膜的主要磨损机制为磨粒磨损,伴有少量的氧化和黏着磨损,316L不锈钢的磨损机制主要为磨粒磨损和塑性变形,伴有少量的氧化和黏着磨损;对磨球为52100钢球时,CrN薄膜的主要磨损机制为黏着磨损,伴有少量的氧化,316L不锈钢的磨损机制主要为黏着磨损,伴有少量的氧化和磨粒磨损。CrN薄膜与两种对磨球的磨损量均小于316L不锈钢基体的磨损量,说明CrN薄膜有效提高了基体的耐磨性。     

Fabrication and Wear Performance of (Cu–Sn) Solution/TiC<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> Bonded Diamond Composites

The Cu(Sn)–TiC_x bonded diamond composites were prepared by in situ reaction sintering of Cu, Ti₂SnC and diamond powders. Effect of Ti₂SnC content on the phase composition, microstructure and grinding properties were studied. The result shows that Ti₂SnC was decomposed to TiC_x and Sn. And then, Sn atom dissolved into the crystal lattice of Cu and formed Cu(Sn) solution. The rich C formed at the interface between diamond and the matrix. Excess Ti₂SnC inhibited the formation of Cu solid solution and reacted with Cu to form Cu₃Sn. Additionally, its matrix was mainly composed of TiC_x with better wear resistance, which may improve obviously the grinding performance of the composites. The grinding ratio value of copper–diamond composite was only 132. The grinding ratio value of the composite contained higher Ti₂SnC content in the raw materials was 636.     

Ni-金刚石复合涂层的结构优化及基础磨削性能

采用电沉积技术在304不锈钢基体上制备了Ni-金刚石复合涂层。通过金刚石掺入量、加厚镀时间优化了金刚石复合涂层结构,利用球-盘式摩擦磨损试验仪研究了优化后的金刚石复合涂层对不同材料偶件(GCr15、SiC、304不锈钢)的磨削性能。结果表明:金刚石掺入量为1.5g/L时,金刚石上砂均匀且密集;加厚镀15min时,金刚石埋入率约为2/3,附着强度较好,适合磨削加工;GCr15、SiC、304不锈钢3种材料偶件的磨损体积依次减小,分别为:0.353 76mm~3、0.315 90 mm~3、0.194 01 mm~3,金刚石复合涂层对GCr15有较好的磨削性能;金刚石复合涂层磨削GCr15、SiC、304不锈钢均发生了磨粒磨损,此外,GCr15还发生了微弱的化学磨损,不锈钢发生了较明显的化学磨损和粘着磨损。     

Effect of Combined Grinding–Burnishing Process on Surface Integrity,Tribological, and Corrosion Performance of Laser-Clad Stellite 21 Alloys

Herein, the influence of the grinding–burnishing on surface integrity, mechanical properties, and corrosion performance of Stellite 21 alloys coating deposited by laser cladding is investigated. The as-clad specimens are first ground followed by further modification by ball burnishing at forces of 424 N and 509 N. Results show that the grinding–burnishing enhances surface finish by lowering R_a from 2.6 to 0.73 μm and R_z from 13 to 4.9 μm, respectively. Surface porosity is found to decrease from 3.8% to 0.9%. Hardness is increased from 609 HV to 702 HV, with a surface alteration as deep as 250 μm, while wear resistance increases by reducing worn volume from 4.15 to 2.95 mm³. Because of high hardness, the grinding–burnishing increases impact resistance by lowering indent depth by 20%. Grains flatten and surface undulations are remarkably reduced due to burnishing. Finally, grinding–burnishing at 509 N improves the corrosion resistance by increasing positive corrosion potential from −0.41 to −0.14 V and lowering corrosion current density from 6.34 × 10⁻⁴ A cm⁻² to 2.19 × 10⁻⁵ A cm⁻², as compared to grinding. This synergistic grinding–burnishing can be a plausible post-treatment route for the laser-clad alloys.     

Media Wear in Stirred Milling

ABSTRACT

A method for measuring media wear using a commercially available 0.751 stirred mill is described. Five material groups, namely steel, ceramics, natural materials, glass, and ore pebbles (autogenous grinding) were tested using water alone and a 60% by weight slurry of sulfide ore. Other variables were stirrer speed and media size. The relative wear rates of the different materials and their effects on grinding efficiency are reported. Relative costs of media were taken into account in the assessment. Ottawa sand was the most cost effective medium for wear, and steel shot for grinding efficiency.     

Grinding abrasive wear and associated particle size effect

Abstract

The type of abrasion that the grinding medium experiences inside a ball mill is classified as high stress or grinding abrasion, because the stress levels at the surface of the medium exceed the yield stress of the metal when hard abrasives are crushed. During dry grinding of ores the medium undergoes not only abrasion but also erosion and impact. As all three mechanisms of wear occur simultaneously, it is difficult to follow the individual components of wear. However, it is possible to show that the overall kinetics of wear follows a simple power law of the type w = at^b, where w is the weight loss of the grinding medium for a specified grinding time t and a and b are constants. Experimental data, obtained from dry grinding of quartz for a wide range of times using AISI 52100 steel balls having various microstructures in a laboratory scale batch mill, are fitted to the proposed equation and the wear rate w is calculated from the first derivative of the equation. The mean particle sizes of the quartz charge D corresponding to 50 and 80% retained size are determined by mechanical sieving of the ground product after a grinding time t and thus the relationship between wear rate and particle size of the abrasive is established. It is found that w increases rapidly with D up to some critical size and then increases at a much lower rate.

MST/1620     

Tribological performance of nano-Al2O3 reinforced polyamide 6 composites

Nano-Al₂O₃ and micron Al₂O₃ reinforced polyamide 6 composites (PA6/Al₂O₃) were prepared via in situ polymerization. The effects of nano-particle content and wear condition on the tribological properties of the composites were measured using a MM-200 block on ring wear tester. The worn surface was investigated with a scanning electronic microscope and a metallurgical microscope and the wear mechanism was proposed. It was found that nano-Al₂O₃ improved the wear resistance of monomer casting polyamide 6 with the optimal content of nano-Al₂O₃ being approximately 3 wt.%. The wear rate of PA6/Al₂O₃ nano-composite was lower than that of the composite with micron Al₂O₃ and increased slowly while its friction coefficient decreased gradually with load. However, the friction coefficient of the composite was somewhat larger than that of monomer casting polyamide 6 and lower than that of the composite with micron Al₂O₃.     

High-speed grinding of isophthalic resin glass fibre reinforced plastic pipes

Abstract

In an experimental investigation some of the parameters affecting the efficiency of cylindrically grinding glass fibre reinforced plastic pipe section have been examined. For a range of grinding conditions, 70% glass isophthalic resin workpieces were ground, using a variety of aluminium oxide and silicon carbide grinding wheels. Such parameters as grinding forces, specific energy, and wheel wear are collated. Also examined was the effect on the grinding parameters and workpieces when the infeed rate is increased, for grinding both with and without coolant.

MST/383     

Effect of magnesium addition on wear behaviour of Al–70 vol.-%Al2O3p composites

Abstract

Inthisstudy, drysliding and abrasive wear behaviour ofAl-70 vol.-%Al₂O₃particulate composite alloyed with Mg was examined. The composites were produced by a pressure infiltration casting technique. The composition of the matrix varied between 0 and 8 wt-%Mg, and the diameter of the Al₂O₃ particulates was 60 μm. Dry sliding wear tests were carried out on an unlubricated M2 quality high speed tool steel disc by a pin on disc type wear tester. Abrasive wear tests were run by rubbing the composites on abrasive Al₂O₃ grains. The results of the wear tests revealed that, both dry sliding and abrasive wear resistance ofthe composites increased with increasing Mg content in the matrix.     

Effect of nozzle angle and depth of cut on grinding titanium under cryogenic CO2

Grinding force and grinding energy are the significant factors associated with the grinding process. The higher heat at the contact zone leads to dulling grits and frequent breakage of grit particle resulting in increase of the grinding force. This problem can be met by bringing down the temperature at the contact zone. The oil-based coolant fails to eliminate the heat at the grinding zone. Hence, the approach of cryogenic coolant is required for this problem. In the present study, an experimental work has been made on the grinding Ti-6Al-4V under cryogenic carbon dioxide (CO₂) and conventional coolant condition. Grinding experiments were performed with an electroplated cubic boron nitride (CBN) wheel, with two factors such as nozzle inclination angle and depth of cut (DOC). The output response parameters considered were surface roughness (R_a), tangential force (F_t), normal force (F_n) grinding zone temperature (GT), and specific energy. The effect of CO₂ and wet coolant on the chip morphology and surface modification in grinding Ti-6Al-4V was analyzed. The experimental result indicates when cryogenic CO₂ was used as a coolant the F_t is reduced from 3 to 21% and 2 to 99% in F_n. The R_a was reduced by 333% and GT by 48% over conventional grinding.     

A novel load-insensitive Co3Mo2Si reinforced in-situ metal-matrix composite coating for wear resistance application

A novel Co₃Mo₂Si/Co_ss in-situ metal-matrix composite coating consisting of hard and strong intermetallic Co₃Mo₂Si and ductile Co solid solution was fabricated by a laser cladding process. The microstructure of the coating was characterized and the wear property was evaluated under dry sliding wear test conditions. Results indicated that the coating displayed very excellent wear resistance, and was extremely insensitive to the load.     

The effect of titanium addition on the microstructure,mechanical and tribological properties of Ni3Si alloys prepared by powder metallurgy method

Ni₃Si alloy with different content of titanium was fabricated by powder metallurgy method. The microstructures, hardness and tribological properties of the alloys were investigation. The results showed that pure Ni₃Si alloy was composed of β₁‐Ni₃Si phase and γ‐Ni₃₁Si₁₂ phase, and Ni₃Ti phase formed with titanium addition. The hardness of the alloy decreased with the increasing titanium content. The friction coefficient of pure Ni₃Si alloy increased with the increasing load, while the friction coefficient of the alloy with titanium addition decreased. The wear rates of the alloys were all increased with increasing load, and the alloy with 5 % titanium addition had the best wear resistance properties. The wear mechanisms of the alloys were abrasive wear at low load, and the wear mechanisms changed to oxidative wear at high load.     

有机复合摩擦材料的成分优化及其对摩擦性能的影响

采用正交试验设计方法对有机复合摩擦材料的成分进行优化,利用MMS-2A摩擦磨损试验机对材料的摩擦系数进行测试,用比磨损率表征复合材料的磨损性能,并通过极差法对试验结果进行了分析。用Leica体式显微镜和3D激光共聚焦显微镜观察了材料摩擦磨损后的表面形貌,探索了不同成分下合成材料的摩擦磨损机理。结果表明:改性酚醛树脂对材料的平均摩擦系数和比磨损率的影响最大。摩擦系数较优的组合为A1B1C2D2,比磨损率较优的组合为A3D1C1B3。树脂含量较少时,摩擦表面的摩擦膜较少,犁沟较深,呈严重的磨粒磨损特征;随树脂含量增加,摩擦表面形成完整且连续的摩擦膜,犁沟较浅,材料的主要磨损形式为粘着磨损和磨粒磨损。     

Relationship between thermal and sliding wear behavior of Al6061/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> metal matrix composites

Al6061 alloy and Al6061/Al₂O₃ metal matrix composites (MMCs) were fabricated by stir casting. The MMCs were prepared by addition of 5, 10 and 15 wt% Al₂O₃ particulates and the size of particulates was taken as 16 μm. The effect of Al₂O₃ particulate content, thermal properties and stir casting parameters on the dry sliding wear resistance of MMCs were investigated under 50–350 N loads. The dry sliding wear tests were performed to investigate the wear behavior of MMCs against a steel counterface (DIN 5401) in a block-on-ring apparatus. The wear tests were carried out in an incremental manner, i.e., 300 m per increment and 3,000 m in total. It was observed that, the increase in Al₂O₃ vol% decreased both thermal conductivity and friction coefficient and hence increased the transition load and transition temperature for mild to severe wear during dry sliding wear test.     

Wear behaviors of Fe-based amorphous composite coatings reinforced by Al2O3 particles in air and in NaCl solution

In this paper, the influence of the addition of Al₂O₃ particles on the microstructure and wear properties of Fe-based amorphous coatings prepared by high velocity oxygen fuel (HVOF) has been studied. The wear behaviors of the composite coatings were evaluated against Si₃N₄ in a pin-on-disk mode in air and in 3.5 wt.% NaCl solution. It was found that the Al₂O₃ particles were homogenously distributed in the amorphous matrix and the composite coatings exhibited improved wear resistance and reduced coefficient of friction (COF) in both air and wet conditions as compared to the monolithic amorphous coating. The composite coating reinforced with 20 wt.% Al₂O₃ particles exhibit the best wear performance, which, for example, has extremely low COF (< 0.2) and high wear resistance (2–3 times higher than monolithic amorphous coating). Detailed analysis on the worn surface indicated that the wear mechanism for the amorphous and composite coatings is similar and is dominated by oxidative delamination in air and by corrosion wear in 3.5% NaCl solution. The enhanced wear resistance is mainly attributed to the addition of Al₂O₃ particles which exhibit high hardness, good corrosion resistance and excellent chemical and thermal stability.     

Evaluation of wear characteristics of Al3Tip/Mg composite

The dry sliding wear tests were performed for a novel developed Al₃Ti_p/Mg composite under the ambient temperatures at 25–200 °C and the loads of 25–150 N. The wear rate of the composite increased with increasing the load, but reduced with increasing the ambient temperature. The Al₃Ti_p/Mg composite had relatively lower wear rates than AZ91D alloy under the loads of less than 100 N at 25 °C. At 200 °C, the Al₃Ti_p/Mg composite presented an absolutely higher wear resistance than AZ91D alloy, and the mild-severe wear transition was delayed. These were attributed to Al₃Ti particulates and the mechanical mixing layer formed on the worn surfaces, which hindered the plastic deformation and thermal softening of the matrix. The mechanical mixing layer contained MgO, Fe–Ti–O, Al₃Ti, Mg₁₇Al₁₂ and Mg and thickened with increasing the ambient temperature. The predominant wear mechanisms of the composite were oxidation wear and delamination wear.     

石墨烯/纳米Al2O3增韧Ti(C,N)基金属陶瓷的力学及摩擦磨损性能

采用真空热压烧结工艺制备了石墨烯(GNPs)和纳米Al₂O₃增韧的Ti(C,N)基金属陶瓷复合刀具材料(TAG)。研究了GNPs和纳米Al₂O₃对复合陶瓷材料微观结构、力学性能和摩擦磨损性能的影响。研究表明,GNPs和纳米Al₂O₃的添加对复合陶瓷材料的力学性能有明显的提高,当GNPs和纳米Al₂O₃含量(质量分数)为1%和5%时,复合刀具陶瓷材料(TA5G1)综合力学性能最优,其硬度、抗弯强度和断裂韧性分别为21.50 GPa、810.80 MPa和10.51 MPa·m^1/2。研究了复合刀具材料的摩擦磨损性能和磨损机理,研究结果表明,在TAG复合刀具材料中,TA5G1的摩擦磨损性能最优,其摩擦系数和磨损率分别为0.338和4.921×10^-6 mm³/(N·m),复合刀具材料的主要磨损形式为磨粒磨损和黏着磨损。     

Processings of iron oxides at room temperature. II. Mechanochemical reaction effects on the structure and surface of pure,synthetic lepidocrocite

The gradual transformation, at ambient temperature, of synthetic crystalline γ-FeOOH during several dry grinding periods in an automatic mortar, has been followed by IR, XRD and surface area analysis. This study shows that as grinding proceeds, parallel to the progressive disappearence of γ-FeOOH, a distinct α-Fe₂O₃ phase is developing. This mechanochemical reaction is completed at 32 hr grinding, when γ-FeOOH is no further detected by IR spectroscopy nor by X-ray powder diffraction. The surface area (So) measurements indicate a decrease of the γ-FeOOH particles size during the early stages of grinding (24 hr); thereafter the So profile is ruled by the surface energy of the formed α-Fe₂O₃ particles. XRD suggests that broadening affects in a non uniform way the peaks describing the α-Fe₂O₃ diffraction planes, the typical 024 plane being the most affected. By analogy with α-FeOOH dry grinding, variations in size, color and eventually in water content are gradually observed during this γ-FeOOH → defect α-Fe₂O₃ mechanochemical decomposition, The latter's mechanism is discussed.