SHS-PHIP法制备TiC-Ni(Mo)金属陶瓷

采用Ti粉、碳黑、Ni粉和Mo粉的混合物，通过自蔓延高温合成(SHS)结合准等静压(PHIP)方法制备了TiC—Ni(Mo)金属陶瓷材料。X射线衍射结果表明，材料由TiC相和Ni合金粘结相组成。扫描电镜观察，球形的TiC颗粒较均匀地分布在Ni合金粘结相中,TiC颗粒尺寸约为2～4μm，在局部较大的TiC颗粒之间存在微孔缺陷。SHS—PHIP法制备的TiC—Ni(Mo)金属陶瓷材料具有良好的致密性和优良的力学性能。     

WC-Co-Ni_3Al基硬质合金微观组织结构分析

通过扫描电子显微镜、X射线能谱仪以及X射线衍射仪等多种仪器分析Ni3Al在硬质合金中的分布区域、晶粒形貌和晶粒大小。通过粘结相相剥离及硬质相剥离处理分析Ni3Al添加量对硬质合金微观结构影响。研究表明:Ni3Al均匀分布于硬质合金粘结相中,未在硬质相WC及粘结相界面处析出,也未在粘结相中富集。通过对粘结相进行浸蚀,发现Ni3Al晶粒形貌为六面体结构,晶粒大小为100 nm左右。Ni3Al添加量影响硬质相WC的晶粒形貌,WC晶粒细化并且表面出现结晶台阶,WC晶粒变为圆钝,随着Ni3Al添加量的增加其变化趋势越明显。     

TiC对WC-13Co细晶粒硬质合金组织和性能的影响

以WC、TiC为硬质相,Co为粘结相,通过湿磨混粉、造粒、模压成形、气氛烧结制备硬质合金材料。通过X射线衍射、SEM、万能材料试验机等方法研究了TiC的添加量对细晶粒硬质合金组织和性能的影响。结果表明:添加TiC可以抑制W在Co中的固溶,提高合金的磁性钴含量;烧结过程中WC和TiC反应生成一种灰色的(Ti,W)C固溶体,具有较高的硬度,随着TiC含量的增加,合金的钴磁、硬度均升高而抗弯强度下降。在裂纹扩展过程中,(Ti,W)C固溶体可以使裂纹发生偏转,延长裂纹扩展路径,同时可以对裂纹起到钉扎作用,对合金有增韧作用。     

Ti(C,N)基金属陶瓷烧结过程中的相变

该文对不同温度下烧结的试样作了X－射线分析，测定了不同温度下，硬质相和粘结相的点阵常数，各主要组成相X射线的相对衍射强度，并对最终烧结体进行了能谱分析。通过以上实验，确定了Ti（C，N）基金属陶瓷烧结过程中所发生的相变、固溶等变化规律。     

烧结气氛对Ti(CN)基金属陶瓷组织和性能的影响

用X射线衍射、背散射扫描电镜及能谱仪等分析手段研究了烧结气氛(真空、N2、Ar)对不同成分TiC基和Ti(CN)基金属陶瓷合金显微组织和性能的影响.金属陶瓷在N2和Ar中烧结后,合金碳含量比在真空中烧结的碳含量低0.5%左右;在N2中烧结后,合金的氮含量提高了0.5%左右.环状结构心部可以是以钨等重金属元素为主要成分的碳化物,也可以是以钛为主要成分的碳化物和碳氮化物.环状结构为金属元素含量和分布不同的(Ti,W,Ta,Mo,Co,Ni)(C,N)固溶体,粘结相是与Ti,W,Ta,Mo,C,N等元素有不同溶解度的钴镍固溶体.真空烧结后组织结构比较均匀,合金的性能最好.在Ar、N2中烧结后,气氛中的氧和氮参加烧结反应,影响合金成分碳氮平衡,在合金表面形成壳层结构,产生表面缺陷,合金的密度、显微硬度、抗弯强度均有比较大的降低;N2气氛影响更大.     

新型W－Ni－Fe－TiB_2合金

讨论了采用高压成型低温烧结技术制造新型高比重钨合金复合材料的方法。通过烧结密度和硬度测定研究了该材料的烧结工艺；利用Ｘ射线衍射仪确定了它的相组成，发现除了Ｗ、γ－（Ｆｅ、Ｎｉ）和ＴｉＢ＿２外，还存在一种生成相ＣｏＷ＿２Ｂ＿２；在扫描电子显微镜下观察发现ＴｉＢ＿２和ＣｏＷ＿２Ｂ＿２相均能较均匀地分布于粘结相内，推断ＴｉＢ＿２和ＣｏＷ＿２Ｂ＿２对材料的粘结相可能起到强化作用。     

新型W—Ni—Fe—TiB2合金

讨论了采用高压成型低温烧结技术制造新型高比重钨合金复合材料的方法，通过烧结密度和硬度测定研究了该材料的烧结工艺，利用Ｘ射线衍射仪确定它的相组成，发现除了Ｗ，γ－（Ｆｅ－Ｎｉ）和ＴｉＢ２外，还存在一种生成相ＣｏＷ２Ｂ２在扫描电子显微镜下观察发现ＴｉＢ２和ＣｏＷ２Ｂ２相均能较均匀地分布于粘结相内，推断ＴｉＢ２和ＣｏＷ２Ｂ２对材料的粘结相可能起到强化作用。     

强磁场作用下Al-Ni合金中Al3Ni析出相的凝固行为

用金相显微镜和X射线衍射研究了强磁场条件下Al-8％Ni合金中非铁磁性的Al3Ni析出相的凝固行为，发现强磁场诱导Al3Ni晶粒以C轴平行磁场方向取向，并且晶粒的长轴与C轴垂直；取向的晶粒在垂直磁场方向上形成多个相互平行的Al3Ni聚合面，即形成规则的Al3Ni层状组织：在层状聚合面中随机分布着多个大的Al3Ni聚合体，聚合体内部的晶粒有序排列。     

WC-Co硬质合金的脆断和粘结相的结构

使用电子探针显微分析和X射线衍射，对WC－Co硬质合金的断口和粘结相进行了较详细地研究，测定了粘结相的相组成和成分，对合金的断口形貌进行了详细研究。对硬质含金脆性机理进行了探讨。     

Al2O3基复相陶瓷共沉淀-水热法制备研究

用共沉淀-水热法制备Ni／ZrO2／Al2O3复相陶瓷粉体，并对烧结体的力学性能和显微形貌进行了讨论。复相粉体的表征采用高分辩透射电镜（HRTEM）和X射线衍射（XRD）等技术。结果表明：在1．4．丁二醇介质中300℃水热条件下自生压高压釜中反应12h成功制备了Ni／ZrO2／Al2O3复合陶瓷粉体，并且测得复相陶瓷体积密度和断裂韧性。通过场发射扫描电镜观察得到烧结体中t-ZrO2颗粒和Ni颗粒的平均尺寸。     

石墨烯涂层刀具的研究现状

针对高效干式切削加工中润滑能力不足,将自润滑性能优良的石墨烯粒子原位生长或者以复合材料的形式沉积于硬质合金刀具基体表面,有望弥补传统干切削中刀具使用寿命和加工性能偏低的不足。介绍了石墨烯材料在金属切削刀具领域中的研究和应用的现状,解读使用不同的工艺制备方法获得原生石墨烯涂层或者石墨烯复合超硬材料,并用其进行金属切削加工和摩擦磨损的试验。结果表明：石墨烯涂层刀具具备优良的润滑性能,能有效降低刀具的摩擦因数和磨损率,提高其使用寿命。     

Surface integrity assessment of laser treated and subsequently coated cemented carbides

Cemented carbides, referred to as hardmetals, are forefront engineering materials widely implemented in industry for chip-removal cutting tools and supporting parts. As a newly developed technology for surface modification with high precision, the application of short pulse laser may extend the utilization of cemented carbides. However, surface integrity of laser-treated materials may be affected during the ablation phenomena. These potential changes may also be relevant for subsequent coating deposition, a surface modification stage usually invoked in many cutting and forming tools. It is the objective of this work to study the influence of a previous laser treatment on the surface integrity of a cemented carbide grade, finally coated by a ceramic layer introduced by physical vapor deposition. In doing so, a nanosecond laser has been employed. Surface integrity is assessed in terms of roughness, hardness, and microstructural changes induced at the subsurface level. It is found that pulse laser can effectively remove the target material, resulting roughness being similar to that attained by abrasive grinding. Although some subsurface damage is observed, it is limited to a very shallow layer, this being thoroughly eliminated during sandblasting implemented before coating deposition. Relative hardness increase is larger for laser treated substrate than for just polished one, reason behind it being speculated to come from the sandblasting stage used for removing damaged layer.     

On the influence of single grit micro-geometry on grinding behavior of ductile and brittle materials

Recently it has been proven that highly engineered grinding/polishing tools can be manufactured with controlled shapes and distributions of abrasives. This research is directed to understand the influence of the shapes of the micro-cutting edges (i.e. circular/square/triangular base frustums generated by laser ablation), emulating grits of these engineered abrasive tools, on the material removal mechanism for workpiece materials of different mechanical properties (ductile – copper, brittle – sapphire). 2D/3D micro-profilometry, scanning electron microscopy supported by sensory signals (e.g. cutting forces) enabled to understand the relationship between the ploughing/shearing of ductile and brittle behaviour materials upon the number and orientation of the cutting edges that emulate the tested single grit shapes. It was found that for copper the increase in number of cutting edges (NoCE) of the grits results in more localised material pile-up and the reduction of plastic deformations with inherent decrease of specific cutting force; nevertheless, it became apparent that to diminish specific cutting forces, both NoCE and effective contact area between the grit and workpiece material need to be considered. For sapphire, shearing/fracturing phenomena were preponderant in the material removal mechanism when using square/triangular shaped grits while major plastic deformations were found for circular base frustum; significant reduction of specific cutting forces were noted with the increase of NoCE. This preliminary work enables the understanding on the implications of using particular grit shapes when utilising the novel edge-controlled grinding/polishing tools for machining ductile/brittle workpiece materials.     

On the machining of alumina and glass

Machining of electrically non-conducting materials like alumina and glass is still a major problem. Electrochemical spark machining (ECSM) process is a potential process for machining these materials. However, ECSM has its own inherent limitations. So far, only ordinary cutting tools have been used during ECSM by previous researchers, but the results obtained are not as good as anticipated. In the present work, electrochemical spark abrasive drilling (ECSAD) experiments have been conducted using abrasive cutting tools, with a view to enhance the capabilities of the process. Use of an abrasive cutting tool, when compared to a conventional cutting tool, has been found to improve the process performance, viz. enhanced material removal and increased machined depth. The workpiece materials used are alumina and borosilicate glass.     

高温合金切削刀具的研究现状及进展

高温合金具有较高的强度、抗高温氧化性等性能,被广泛应用于各种领域中,其加工时切削温度高、加工硬化严重、刀具磨损严重,是最难加工的材料之一。本文综述了国内外高温合金切削刀具的研究现状。阐述了高温合金的切削特性,重点对高速钢、硬质合金、涂层硬质合金、陶瓷、PCVB这几类高温合金切削刀具材料的研究现状进行了分析;同时,也对国内外切削高温合金刀具的结构、切削加工工艺参数以及磨损机理的研究现状进行了概述。在此基础上,发现高温合金切削刀具虽然已经研发设计出了多种新刀具材料、新切削工艺参数,但仍然需要进一步了解影响刀具性能的因素及刀具磨损机理。因此,本文提出了建立评估刀具使用性能体系和研发高性能的刀具材料是高温合金切削刀具的主要研究方向。     

Nanocrystalline diamond coating tools for machining high-strength Al alloys

Diamond coating tools have been increasingly used for machining advanced materials. Recently, a microwave plasma-assisted chemical vapor deposition (CVD) technology was developed to produce diamond coatings which consist of nano-diamond crystals embedded into a hard amorphous diamond-like carbon matrix. In this study, the nanocrystalline diamond (NCD) coating tools were evaluated in machining high-strength aluminum (Al) alloy. The conventional CVD microcrystalline diamond coating (MCD) tools and PCD tools were also tested for performance comparisons. In addition, stress distributions in diamond coating tools, after deposition and during machining, were analyzed using a 2D finite element (FE) thermomechanical model.

The results show that catastrophic failures, reached in all except one machining conditions, limit the NCD tool life, which is primarily affected by the cutting speed. In addition, coating delamination in the worn NCD tools is clearly evident from scanning electron microscopy (SEM) and force monitoring in machining can capture the delamination incident. At a high feed, coating delamination may extend to the rake face. Furthermore, SEM observations of coating failure boundaries show intimate coating-substrate contact. Though the NCD tools are inferior to the PCD tools, they substantially outperform the MCD tools, which failed by premature delamination. The diamond coating tools can have high residual stresses from the deposition and stresses at the cutting edge are highly augmented. Further machining loading causes the stress reversal pattern which seems to correlate with the tool wear severity.     

Machinability of BN free-machining steel in turning

In the past few years, extensive researches have been done to improve the machinability of work materials in order to increase productivity and reduce the effect on the environment. To satisfy these demands, various free-machining steels have been researched and developed. One of them is BN free-machining steel that contains hexagonal boron nitride (h-BN). However, the machinability was not stable. In this study, machining tests were carried out to clarify the machinability of steels and appropriate chemical composition of work material and tool material to achieve high efficient machining. Tested work materials were plane carbon steel JIS S45C and BN free-machining steels. The JIS S45C was used as the standard. The tool wear in turning BN free-machining steel was smaller than that in turning standard steel. In case of turning BN1 with P30 at 200, 300 m/min, the wear progress rate of flank wear and crater depth were about half as much as that in turning standard steel. BN free-machining steel showed slightly lower cutting temperature and smaller cutting force in comparison with standard steel at the tested cutting speeds. Al and N were detected as a layer at the tool wear region of P grade carbide tools after turning BN free-machining steel at high cutting speed. It is thought that one of the main reasons of outstanding machinability of BN free-machining steel is that the deposited layer containing Al and N acts as diffusion barrier at the tool–chip interface. In turning larger Al content BN-added steel with higher Ti content cutting tools, a larger wear reduction was observed. Therefore, it is said that not only added BN but also appropriate Al is necessary in work material.     

液相辅助激光加工织构微观形貌变化及其影响机制

刀具的快速磨损是制约金属切削效率和加工质量的关键因素,为了增强刀具的耐磨性,延长刀具使用寿命,提高工件的加工质量,通过试验探究液相辅助激光加工织构形貌的特征,分析激光加工参数、液体种类和织构形状对所加工织构质量的区别。结果表明：扫描速度对织构形貌影响较大,硝酸和氢氟酸混合溶液辅助下加工的织构形貌较好,液相辅助激光加工技术更适用于无特定形状的大面积织构加工。     

Failure mechanisms of TiB2 particle and SiC whisker reinforced Al2O3 ceramic cutting tools when machining nickel-based alloys

In this paper, Al₂O₃/TiB₂/SiC_w ceramic cutting tools with different volume fraction of TiB₂ particles and SiC whiskers were produced by hot pressing. The fundamental properties of these composite tool materials were examined. Machining tests with these ceramic tools were carried out on the Inconel718 nickel-based alloys. The tool wear rates and the cutting temperature were measured. The failure mechanisms of these ceramic tools were investigated and correlated to their mechanical properties. Results showed that the fracture toughness and hardness of the composite tool materials continuously increased with increasing SiC whisker content up to 30 vol.%. The relative density decreased with increasing SiC whisker content, the trend of the flexural strength being the same as that of the relative density. Cutting speeds were found to have a profound effect on the wear behaviors of these ceramic tools. The ceramic tools exhibited relative small flank and crater wear at cutting speed lower than 100 m/min, within further increasing of the cutting speed the flank and crater wear increased greatly. Cutting speeds less than 100 m/min were proved to be the best range for this kind of ceramic tool when machining Inconel718 nickel-based alloys. The composite tool materials with higher SiC whisker content showed more wear resistance. Abrasive wear was found to be the predominant flank wear mechanism. While the mechanisms responsible for the crater wear were determined to be adhesion and diffusion due to the high cutting temperature.     

Mechanics of machining of face-milling operation performed using a self-propelled round insert milling cutter

There has been a renewed interest in the technology of rotary tools because of their ability to perform more productive machining and the concurrent evolution of a number of new ‘difficult-to-machine’ materials. This paper presents an investigation into the application of rotary tools in a face-milling operation. The work involved analysis of cutting forces and chip characteristics, and the development of analytical as well as conceptual models to predict the cutting forces. It was evident that the proposed model predicts cutting force magnitude with a fair accuracy.