High-Temperature Sliding Wear Testing of Cathodic Arc Physical Vapor Deposition AlTiN- and AlTiON-Coated Hot Work Tool Steels

Thin hard coatings provide the much needed protection for steel thixoforming tools that must resist wear at high temperatures. The wear resistance of AlTiN- and AlTiON-coated hot work tool steel was investigated at 1023 K (750 °C), measured to be the cavity surface temperature shortly after the steel slurry was forced into the thixoforming die. The wear tests were repeated in exactly the same fashion with uncoated tool steel samples to identify the impact of AlTiN and AlTiON coatings on the high-temperature wear performance of X32CrMoV33 tool steel. The nature, the thickness, and the adherence of the oxide scales impact the tribological behavior. The poor adherence and limited ductility of ferrous oxides promote the failure of the oxide scale impairing the resistance to wear of the hot work tool steel at elevated temperatures. The substantial softening in the X32CrMoV33 hot work tool steel is also critical in the wear volume loss it suffers. AlTiN and AlTiON coatings, on the other hand, form a stable and protective oxide surface layer at high temperatures and therefore provide an enhanced resistance to oxidation. The latter is relatively more resistant to oxidation and is thus the better of the two coatings tested in the present work.     

基于圆环压缩和挤压–模拟法的Zr-4合金塑性成形摩擦因子测定

采用圆环压缩法和挤压–模拟法测定Zr-4合金有润滑条件下的摩擦因子,讨论了2种方法所测定摩擦因子存在差异的原因。研究结果表明,在模具（砧面）粗糙度Ra = 0.6 μm、实验温度700～800 ℃的条件下,采用圆环压缩法获得的Zr-4合金与模具的摩擦因子为0.18～0.27,摩擦因子随实验温度的升高而增大。挤压温度为750 ℃时,采用挤压–模拟法获得的热挤压平均摩擦因子为0.35。测试结果存在较大差异的原因,是由于挤压过程润滑剂的剪切速率较圆环压缩实验大得多,且挤压过程中润滑剂所受压应力约为圆环压缩实验中的两倍,从而导致润滑剂黏度的增大,表现为摩擦因子较高。圆环压缩法获得的摩擦因子更适合于Zr-4合金的锻造等热加工工况。      

7075铝合金板材热冲压成形中的高温摩擦

采用自制的板带高温摩擦试验机模拟实际固溶–冲压–淬火一体化热成形工艺下7075铝合金的高温摩擦过程,分别对上下摩擦头进行冷却和加热以模拟实际热冲压过程对模具和压边圈的冷却和加热,分析了下模加热温度、法向载荷和滑动速度对7075铝合金摩擦行为及磨损机理的影响。结果表明:铝合金摩擦系数随着下模加热温度的升高而增大,磨损机制由300 ℃时的黏着磨损转变为500 ℃时的黏着磨损、氧化磨损和磨粒磨损;施加法向载荷越大,摩擦系数越大,不同载荷下磨损机制均为黏着磨损及轻微的磨粒磨损,且随着载荷增大,黏着磨损程度有所加深;高滑动速度导致了磨损表面局部氧化物的生成,使摩擦系数随着滑动速度增大而减小,滑动速度为30 mm·s?1时,磨损机制主要是氧化磨损、磨粒磨损和黏着磨损。      

Research on microstructure and high-temperature friction and wear properties of a cobalt-based alloy for hot extrusion die

The hot extrusion die is a key tool for determining the surface quality and dimensional accuracy of extruded products.Because its service process is subject to high temperature,high pressure,and wear,it must be resistant to these conditions.In this paper,the high-temperature friction and wear properties of a cobalt(Co)-based alloy were investigated and compared with those of a titanium carbide(TiC)cemented material.The results show that the high-temperature wear performance of the Co-based alloy is better than that of the TiC cemented material,and that Co-based materials have the potential for replacing TiC cemented materials as hot-extrusion-die materials.Due to the high density and good combination of the matrix and carbide,the carbides do not easily peel off from the matrix during the wear process.Due to the higher impact toughness of the Co-based alloys,microcracks that can cause worn-surface peeling are not easily generated.As a result,the high-temperature wear performance of Co-based alloys is found to be better than that of TiC cemented materials.     

Role of Tool Shoulder Diameter in Friction Stir Welding: An Analysis of the Temperature and Plastic Deformation of AA 2014 Aluminium Alloy

The influence of tool shoulder diameter and its rotational speed on the high temperature plastic deformation of the material during friction stir welding of AA 2014 aluminum alloy is investigated, using the principles of hot working. The soundness of weld and defect formation are analyzed using the Zener–Hollomon parameter ‘Z’ to describe the high temperature plastic deformation behaviour of material, under the simultaneous influence of temperature and strain-rate. The observed hot deformation behaviour is correlated with the deformation processing map for the first time. At a given rotational speed, the volume of shoulder driven flow reduces with increasing shoulder diameter.     

Deformation of a surface layer and coating application using a flexible tool

The microstructure and properties of the functional coatings formed by impact friction processing of product surfaces with a flexible tool are studied. It is established that the processing produces a hard nanostructured surface layer with fragments up to 0.13 µm in size, as it is achieved by severe plastic deformation.     

两种热作模具钢的高温摩擦磨损性能

采用高温摩擦磨损试验机研究了HTCS-130和DAC55两种热作模具钢在100~700℃范围内的耐磨性差异及磨损机制, 并结合X射线衍射仪(XRD)、扫描电子显微镜(SEM)、光学轮廓仪等手段对表面相组成、磨损表面、截面形貌等进行分析. 结果表明: 两种钢的磨损率均在100~700℃范围内呈现先增后减的趋势; 其磨损机制表现为在100℃和300℃分别发生黏着磨损和黏着-轻微氧化磨损; 500℃时磨损机制转变为单一氧化磨损, 磨损表面氧化层由FeO、Fe₂O₃和Fe₃O₄组成, 亚表面发生轻微软化并出现塑性变形层; 700℃时磨损进入严重氧化磨损阶段, 氧化物数量急剧增多, 同时由于马氏体基体回复导致材料出现严重软化, 磨损表面形成连续的氧化层. HTCS-130钢优异的热稳定性能使得基体具有较高硬度和更窄的摩擦软化区, 能够更好地支撑氧化层, 从而在700℃下比DAC55钢更耐磨.      

感光鼓用铝管挤压温度场数值模拟与研究

本文使用基于有限体积法的MSC.Superforge软件对感光鼓用铝管挤压过程进行了数值模拟,使用欧拉法表征了挤压过程中金属的温度场。研究了在不同预热温度下坯料的挤压温度分布情况;研究了坯料温度从非稳态到稳态的转变过程,得出了金属在挤压筒与分流组合模焊合室内部的温度变化规律。研究表明在铝管挤压时,由于存在大量变形热和摩擦热而使坯料温度升高;同一预热温度的坯料各部位的温升不相同;不同预热温度的坯料温升也不相同;在其它条件不变的情况下,预热温度越高则坯料温升幅度越小。     

通过等离子渗碳/CrN覆层改性处理提高Ti-6Al-4V合金的耐磨性和抗疲劳特性

In this study, a newly developed duplex coating method incorporating plasma carhurization and CrN coating was applied to Ti-6AI-4V and its effects on the wear resistance and fatigue life were investigated. The carburized layer with approximately150μm in depth and CrN coating film with 7. 5 μm in thickness were fomled after duplex coating. Hard carbide particles such as TiC And V4C3 were formed in the carburized layer. XRD diffraction pattern analysis revealed that CrN film had predominant [111] and [200] textures. The hardness (Hv) was significantly improved up to ahout 1960 after duplex coating while the hardness value of original Ti-6Al-4V was 402. The threshold load for the modification and/or failure of CrN coating was measured to be 32 N using the acoustic emission technique. The wear resistance and fatigue life of duplex coated Ti-6Al-4V improved significantly compared to those of un-treated specimen. The enhanced wear resistance can be attributed to the excellent adhesion and improved hardness of CrN coating film for the duplex coated Ti-6Al-4V. The initiation of fatigue cracks is likely to be retarded by the presence of hard and strong layers on the surface, resulting in the enhanced fatigue life.     

Evaluation of deterioration mechanisms and roll life of different roll materials

Evaluation of wear loss of rolls in operation is very difficult since the rolling conditions are hard to keep under control. To solve this problem a high temperature test rig was designed. A conventional roll material was compared to a hot work tool steel. The main wear mechanisms were different. The conventional roll grade was mainly subjected to thermal fatigue as could be expected. The hot work tool steel was mainly subjected to abrasive wear, and no evidence of thermal fatigue was found. The rate of material loss was 6 times higher in the hot work tool steel, but when the deterioration caused by thermal fatigue of the cast iron is taken into consideration, the deterioration rate was of the same order in both materials. The friction between the hot steel and the roll materials were of the same order. The frictional value should be a measure of the wear rate. Since the wear mechanisms are not equal, the coefficient of friction found in the test rig is only qualitatively related to roll wear.     

Effect of Tooling Temperature on the Transient Lubricant Behavior in Hot Metal Forming Processes

In hot metal forming processes, the temperature of the forming tool progressively increases under serial production conditions. Water-based two-phase lubricants may be applied to cool the forming tool and moderate temperature, in which the liquid agent would evaporate or decompose rapidly with dry matter deposited on the tooling surface during the dwelling time before the forming process commences. Herein, an interactive friction model for a two-phase lubricant is developed to predict the transient lubricant behaviors, i.e., predicting the effects of tool temperature and dwelling time on the friction coefficient evolution and lubricant breakdown. Friction tests between a warm pin and hot aluminum workpiece are conducted using the advanced friction testing system, TriboMate, to validate the modeling results.     

20CrNi2Mo钢干摩擦磨损行为及次表层马氏体形变

 利用MMU-10试验机,在0.13 m/s的速度下,分组对20CrNi2Mo盘环对摩试样进行100、120、150 N接触载荷下的干滑动摩擦磨损试验。采用SEM、EDS、EBSD表征摩擦磨损后环试样表面和截面的形貌及元素。结果表明,接触载荷为150 N时摩擦因数最低、磨损量最大。摩擦热导致磨损表面出现严重的氧化和脱落材料焊结现象,磨损机制由氧化磨损、磨粒磨损和黏着磨损构成。磨损导致了次表层组织变化,出现严重塑性形变层和马氏体形变层。截面EBSD分析结果反映了表层至次表层的应变,EBSD菊池花样质量从表面朝深度方向逐渐提升,采用EBSD图像分割处理及Band Contrast平均值求解可准确找出磨损导致的形变层终止区域。     

Finite Element Analysis of Die Geometry and Process Conditions Effects on Equal Channel Angular Extrusion for β-Titanium Alloy

 The finite element analysis was applied to evaluate the respective influences of die geometry and process conditions on plastic strain distribution for β-titanium (Ti-13V11Cr3Al) alloy during the equal channel angular extrusion (ECAE). It was found that optimum equal channel angular extrusion die geometry is strongly material dependent. Optimal strain homogeneity in the Ti-13V11Cr3Al alloy may be achieved at r (inner radius)=5 mm, R (outer radius)=3 mm. The equivalent plastic strain increases with increasing friction coefficient. And the better homogeneity of the equivalent plastic strain distribution can be achieved when friction coefficient value is lower. The faster the ram speed is, the lower the homogeneity of the equivalent plastic strain distribution is and the influence is slight. The back-pressure does not help to improve the plastic strain homogeneity, and the increasing temperature has a slightly favourable effect on the plastic strain homogeneity between 400 and 600 ℃.     

Tribological Properties of CrN Coated H13 Grade Tool Steel简

The characteristics of CrN coated martensitic H13 grade tool steels were studied. CrN coatings were depos- ited by the arc physical vapor deposition （PVD） before and after the pulse plasma nitriding of the samples. The PVD and plasma nitriding techniques were applied in relevant workshops by following the commercial practice parameters. Experimental results showed that CrN coating deposited on the nitrided surfaces exhibited superior scratch and wear resistances as compared to that deposited on the original martensitic surface.     

High Temperature Tribological Studies on Surface Engineered Tool Steel and High Strength Boron Steel

The popularity of hot sheet metal forming processes in the recent years has necessitated research efforts to improve tool life and control the friction level during hot forming operations. In this work, the tribological properties of tool steel and ultra high strength boron steel (UHSS) pairs at elevated temperatures have been studied by using a special hot sheet metal forming test rig that closely simulates the conditions prevalent in the real process. This test involves linear unidirectional sliding of a preheated UHSS sheet between two tool steel specimens where new workpiece material is continuously in contact with the tool surface. The study is aimed at investigating different surface treatments/coatings applied on either the tool or sheet surface or on both. The results have shown that it is possible to control the coefficients of friction through surface treatments and coatings of the tool and workpiece materials. The application of a coating onto the sheet material has a greater influence on the friction compared to changing the tool steel surface. After running‐in, the investigated tool steel variants show almost similar frictional behaviour when sliding against the same sheet material. Although coating the UHSS sheet reduces friction, it abrades the tool surface and also results in transfer of the sheet coating material to the tool surface.     

Wear mechanism maps for thermal-spray steel coatings

Wear mechanisms in low-carbon-steel-based thermal-spray coatings deposited on aluminum alloys using a plasma-transfer wire-arc (PTWA) process and a high-velocity oxy-fuel (HVOF) process were studied. The coatings investigated consisted of PTWA 1020, HVOF 1020 deposited from a low-carbon steel wire stock, and HVOF 1020-2.5 pct Al produced using a wire stock with 2.5 wt pct Al added to the base AISI 1020 composition. Wear tests were performed using a pin-on-disc-type tribometer equipped with an environmental chamber within a load range of 5 to 75 N and a sliding-speed range of 0.2 to 2.5 m/s against tool steel pins in a dry air atmosphere (10 pct relative humidity). The wear rates of the three types of thermal-spray coatings and the micromechanisms that control the wear rates at different loads and sliding speeds were presented in the form of wear maps. Under dry sliding conditions, two basic wear and surface-degradation mechanisms were identified, consisting of (1) mechanical wear, which involved severe plastic deformation of the iron splats on the contact surfaces and their fracture and (2) oxidational wear that took place by the formation of various iron oxides, whose compositions and thicknesses depended on the loading conditions. The wear rates of PTWA 1020 and HVOF 1020-2.5 pct Al decreased with increasing sliding speed, as they showed a transition from mechanical wear to mild oxidation wear. The wear rates of HVOF 1020 also decreased with increasing speed, but they increased again, once they passed through a minimum where a transition from mild to severe oxidational wear occurred. An improvement in the wear resistance of HVOF 1020 was observed, in particular at high loading conditions, as a result of the addition of 2.5 pct Al to the wire feed stock. The wear maps demonstrated that the wear rates were sensitive to the compositions of the coatings and, hence, to the thermal-spray technique used in their production.     

硬质合金螺旋立铣刀刀片的热挤压成形

本文介绍了采用热挤压方法研制硬质合金螺旋立铣刀刀片的过程,并从理论上分析讨论了钨钴硬质合金的变形属性。认为钨钴硬质合金在高温下有较好的变形能力,热挤压工艺适合于一些特殊形状的硬质合金制品的成形。     

铝合金圆棒挤压过程应力场模拟

以铝圆棒的挤压生产为研究对象,考虑了热传导、对流换热、摩擦生热、塑性功、热力藕合等多种条件,运用Marc软件中的刚塑性有限元分析软件研究了铝圆铸锭挤压生产圆棒过程,模拟分析了摩擦条件和挤压比对应力、应变的影响。     

Microstructural evolution of Al-Si coating and its influence on high temperature tribological behavior of ultra-high strength steel against H13 steel

Al-Si coated ultra-high strength steel(UHSS)has been commonly applied in hot stamping process.The influence of austenitizing temperature on microstructure of Al-Si coating of UHSS during hot stamping process and its tribological behavior against H13 steel under elevated temperature were simulatively investigated.The austenitizing temperature of Al-Si coated UHSS and its microstructual evolution were confirmed and analyzed by differential scanning calorimetry and scanning electron microscopy.A novel approach to tribological testing by replicating hot stamping process temperature history was presented.Results show that the hard and stable phases Fe_2Al_5+FeAl_2 formed on Al-Si coating surface after exposure to 930°C for 5 min,which was found to be correlated to the tribological behavior of coating.The friction coefficient of coated steel was more stable and higher than that of uncoated one.The main wear mechanism of Al-Si coated UHSS was adhesion wear,while abrasive wear was dominant for the uncoated UHSS.