GH4049高温合金在表面不同状态下的残余应力

采用扩展扫描方法在X射线衍射应力分析仪上测定了由GH4049高温合金所制叶片表面铣加工、磨加工、表面吹砂和表面渗铝等不同状态下的表面残余应力。结果表明,铣加工产生了残余拉应力而磨加工和表面渗铝产生了残余压应力。     

3D modeling of residual stresses induced in finish turning of an AISI304L stainless steel

This paper addresses the development of a new methodology predicting residual stresses induced in finish turning of a AISI304L stainless steel. A hybrid approach combining experimental results and a numerical model is applied. The model simulates the residual stresses generation by applying equivalent thermo-mechanical loadings onto the machined surface without modeling the chip removal process, which enables rapid calculation. The shape and the intensity of equivalent thermo-mechanical loadings are identified through experimental measurements. Friction tests enable to model the thermal and mechanical loadings along the tool-workmaterial interface. Orthogonal cutting tests provide thermal and mechanical loadings below the primary and third shear zone. This model has already been presented in several papers, but only in a 2D configuration. The objective of this paper is to transfer this hybrid approach into a 3D configuration, which is closer to a concrete longitudinal turning operation. Based on this new model, the paper aims at investigating the interactions between each revolution. It is shown that around five revolutions are necessary to reach a steady state. Finally numerical results are compared with experimental measurements obtained by X-Ray diffraction. It is shown that residual stresses cannot be considered as homogeneous over the surface due to tool's feed. Additionally, the X-Ray beam is much too large to be able to quantify this heterogeneity. Based on average numerical values coherent with average values obtained by X-Ray diffraction, it is shown that the numerical model provides consistent results compared to experimental measurements for a large range of cutting speed and feed.     

An investigation of surface damage in the high speed turning of Inconel 718 with use of whisker reinforced ceramic tools

The paper presents the results of an investigation of surface damage produced by whisker-reinforced ceramic cutting tools in the finish turning of Inconel 718. The effects of the cutting parameters, of the tool wear and of the coolant condition on damage to the machined surface was investigated experimentally. The surface generated by machining was examined by use of both a scanning electron microscope (SEM) and a high resolution scanning electron microscope (HRSEM). This showed the regions of the surface that were damaged to contain both geometric defects and changes in the metallurgical structure of the subsurface. The types and the extent of the surface damage were found to be dependent upon the cutting parameters, the size of the wear land and the coolant conditions. The extent and the character of the coarse-scale and the fine-scale damage were analyzed on 72 specimens for which the cutting speeds, feed rates and coolant conditions (wet and dry) and the degree of tool wear differed. The types of damage that occurred in the form of micro-cracking and breakage, plastic flow, cavities, side flow and built-up edges are discussed.     

Residual stresses in cold-wire gas metal arc welding

This work compares the welding residual stresses of the cold-wire gas metal arc welding and conventional gas metal arc welding processes. Two techniques were used to measure the residual stresses: X-ray diffraction and acoustic birefringence. The base metal used was carbon manganese steel plates of 9.5-?mm thickness. The results showed that the introduction of the cold-wire tends to decrease the residual stresses, suggesting that the introduction of the cold wire decreases the amount of heat given to the base metal, and consequently lowers residual stresses.     

Residual stresses in titanium nitride thin films obtained with step variation of substrate bias voltage during deposition

In this work, a series of depositions of titanium nitride (TiN) films on M2 and D2 steel substrates were conducted in a Triode Magnetron Sputtering chamber. The temperature; gas flow and pressure were kept constant during each run. The substrate bias was either decreased or increased in a sequence of steps. Residual stress measurements were later conducted through the grazing X-ray diffraction method. Different incident angles were used in order to change the penetration depth and to obtain values of residual stress at different film depths. A model described by Dolle was adapted as an attempt to calculate the values of residual stress at each incident angle as a function of the value from each individual layer. Stress results indicated that the decrease in bias voltage during the deposition has produced compressive residual stress gradients through the film thickness. On the other hand, much less pronounced gradients were found in one of the films deposited with increasing bias voltage.     

Effects of electrical discharge surface modification of superalloy Haynes 230 with aluminum and molybdenum on oxidation behavior

The effects of the electrical discharge alloying (EDA) process on improving the high temperature oxidation resistance of the Ni-based superalloy Haynes 230 have been investigated. The 85 at.% Al and 15 at.% Mo composite electrode provided the surface alloying materials. An Al-rich layer is produced on the surface of the EDA specimen alloyed with positive electrode polarity, whereas, many discontinuous piled layers are attached to the surface of the EDA superalloy when negative electrode polarity is selected. The oxidation resistance of the specimen alloyed with positive electrode polarity is better than that of the unalloyed superalloy, and the effective temperature of oxidation resistance of the alloyed layer can be achieved to 1100 °C. Conversely, the oxidation resistance of the other EDA specimen alloyed with negative electrode polarity is even worse than that of the unalloyed superalloy.     

Residual stresses in wires: Influence of wire length

Residual stresses are one of the causes of failures in structural components. These stresses may arise in the fabrication process from many causes. They cannot be easily accounted for because they are both difficult to predict and to measure. X-ray diffraction (XRD) is nowadays a widespread technique for measuring surface residual stresses in crystalline materials. Very small specimens are often used for this purpose due to geometrical restrictions of either the diffractometer sample holder or the component to be inspected. However, the cutting process itself may affect the residual stress state in these specimens, so measured stresses could be misleading. In this work, the influence of specimen length on residual stresses was investigated in cold-drawn ferritic and pearlitic steel wires by XRD measurements and finite element simulations. In the ferritic wires, numerical simulations coincide with experimentally measured stresses. However, in the pearlitic wires the effect of the stresses in cementite (which could not be measured by XRD) has to be taken into account to explain the observed behavior. The results obtained have shown that in both materials the cutting process affects residual stresses, so it is recommended that specimens larger than five times the wire diameter be used.     

薄壁Ti6Al4V管件采用不同车削参数加工引起的表面残余应力的测量

切削加工引起的金属零件的表面残余应力,其性质和大小对零件的服役性能产生很重要的影响。在测量车削加工Ti6Al4V薄壁管件引起的表面残余过程中,由于边缘效应的存在,使得零件的长度对测量精度有严重的影响。由于管件的壁厚很薄,当去除一应力层时会对剩余部分的残余应力的重新分布产生重要的影响,因此必须对剥层后X射线法测得的应力值进行修正补偿才能得到其初始应力值。传统的修正方法其计算比较复杂,对零件和应力都有特别的要求,而且在某些情况下其修正精度还达不到要求。同时考虑测量精度、测量可行性以及节约材料诸多方面的问题,本文运用有限元验证的方法确定零件合适的长度。同时本文运用精度较高的基于有限元分析的修正方法结合X射线法测量Ti6Al4V管件车削加工引起的表面残余应力,分析不同切削参数以及退火处理对表面残余应力的影响。结果显示：切削速度、进给量以及切削深度在指定范围内增大时会导致表面切削和进给方向的压应力增大,退火处理会使得表面两个方向的残余应力减小将近85%。     

PcBN刀具车削镍基高温合金切削性能研究

本文研究了刀尖圆弧半径、负倒棱参数、切削速度、PcBN材质及干湿切削对PcBN刀具车削镍基高温合金GH4169切削性能的影响.试验结果表明:增大刀尖圆弧半径、负倒棱角度或减小负倒棱宽度均会使刀具磨损相应减小;PcBN的磨损随切削速度的提高而增大;DBW85的切削性能优于BZN6 000和BTN100,且其高速下的磨损量...     

Investigation of heat partition in high speed turning of high strength alloy steel

High Speed Machining (HSM) is now recognised as one of the key processes in advanced machining technology for automotive, die and mould, and aerospace industries. Machining of metals at high cutting speeds produces high temperatures in the primary shear zone, which induces plasticity in the workpiece and hence decreases the cutting forces. This investigation is concerned with the estimation of the amount of heat flowing into the cutting tool in high speed turning of BS 970-709M40EN19 (AISI/SAE-4140) high strength alloy steel. The aim is to characterise the thermal field in the cutting zone and thus understand the mechanics of HSM. Experimental results are presented of temperature measurements on the tool rake face during orthogonal cutting at cutting speeds ranging between 200 and 1200 m/min. These measured temperatures are compared with temperature fields in the cutting tool obtained from a finite element transient thermal analysis. It is shown that the tool–chip contact area, and hence the proportion of the secondary heat source conducting into the tool, changes significantly with cutting speed; it decreases with the cutting speed in the conventional and the transition regions but increases in the HSM region approaching 65% at 1200 m/min. These results are relevant to the study of thermal expansion of the cutting tools and the cutting edge wear in HSM operations.     

Evolution of micro-pores in a single crystal nickel-based superalloy during 980°C creep

The evolution of micro-pores in a single crystal nickel-based superalloy during creep at 980 °C/220 MPa was investigated by X-ray computed tomography. Time-dependent ex-situ 3D information including the number, volume fraction, distribution and morphology of micro-pores was analyzed. The results reveal that the signifi cant formation and growth of micro-pores occur at the end of secondary/beginning of tertiary creep stage. The irregular large pores as well as high density pores located at strain...     

Residual stresses,microstructure and tensile properties in Ti–6Al–4V friction stir welds

Abstract

This paper reports the results of a systematic investigation of residual stresses as a function of welding speed in a set of Ti–6Al–4V friction stir welds. The investigation focuses on residual stress but links these data with microstructural information derived from micrographs and hardness measurements as well as mechanical testing results. Residual stresses were determined using energy dispersive synchrotron X-ray diffraction, which allows phase specific stresses to be distinguished. The data presented in this paper demonstrate that welds with high tensile properties can be obtained, which also have relatively low peak tensile residual stress values of ～30% of the tensile strength. The data also show a clear correlation between heat input and the width of the residual stress profile.     

强磁场下时效处理对铸造镍基高温合金K52中碳化物的影响

针对时效处理铸造镍基高温合金K52的碳化物,研究了其在强磁场作用下的组织形貌与化学成分变化规律。结果表明:在不同磁场条件下时效处理后,合金中碳化物MC和M23C6的组织形貌与分布基本相同,强磁场的施加对碳化物的组织形貌与分布并未产生显著影响,但经强磁场条件下时效处理后,MC和M23C6中强碳化物形成元素W、Mo、Nb和Ti含量有所增加,而弱碳化物形成元素Cr和非碳化物形成元素Co、和Ni含量显著降低。分析指出强磁场的施加可能提高了强碳化物形成元素与C间的亲和力,增强了其形成碳化物的倾向;同时其可能减弱了弱碳化物形成元素和非碳化物形成元素与C间的亲和力,从而使其在碳化物中存在的倾向也进一步降低。     

Development of high strength stainless steel brazed joints using rapidly solidified filler alloys

Abstract

Two types of rapidly solidified filler alloys of nominal composition Cu–40Mn–10Ni (C50) and Ni–7Cr–3·2B–4·5Si–3Fe (N82) were used for stainless steel (SS304) brazing joints. The C50 foil is crystalline in nature, whereas N82 foil shows amorphous structure. The SS304/C50/SS304 joint shows solid solution phases at interfacial area, with maximum bond strength of 500 MPa, which qualifies to 80% of base metal strength. Conversely, the SS304/N82/SS304 joint develops brittle Cr_xB_y intermetallic phases, which lowers bond strength to 330 MPa.     

单晶结构残余应力的X射线衍射分析技术

准确测定单晶材料残余应力是控制和调整单晶构件中残余应力的前提。基于弹性力学对单晶材料弹性模量与对应衍射晶面的关系进行理论分析,建立立方单晶材料的残余应力分析模型,并提出具体试验方法,以DD3单晶叶片为例,进行试验验证。结果表明：不同衍射晶面的弹性模量受独立弹性柔度系数、取向系数影响,DD3单晶叶片表面应力模型计算值与实测值间相对误差在20 MPa范围内。这种X射线衍射残余应力测定方法测定的残余应力值可靠性较高,为工程应用中测定立方单晶残余应力提供了理论依据和试验基础。     

Study on the distribution of residual stresses in linear friction welds of Ti6Al4V

The linear friction welding process of Ti6Al4V was modeled and computed for obtaining the residual stresses.Temperature,stress and strain fields were simulated,based on which,the residual stresses were...     

应力振动快速调整处理对铸铁轧辊表面残余应力的影响

利用X-射线衍射法测定了应力振动快速调整处理前、后φ800mm铬钼冷硬球墨复合铸铁轧辊表面的残余应力及衍射峰半高宽变化情况，结果表明：应力振动快速调整处理能有效地降低和均化铸铁轧辊表面残余应力，通过衍射峰半高宽的增大现象阃接反映轧辊表面产生了微观塑性变形及位错密度的增大。     

Residual stress relaxation during heating of bearing rings produced in two different manufacturing chains

Bearing rings produced in two different manufacturing chains have been investigated in terms of residual stress relaxation behavior during heating. Cold rolled rings present almost constant compressive residual stresses at the external periphery and completely affected cross sections. Machined rings show high tensile residual stress with periodic variations along the outer periphery caused by clamping during machining. Residual stress states then are confined in a very thin layer. With increasing temperature residual stresses relax. Machined rings present a progressive loss of the residual stress periodicity with increasing temperature. The cold rolled rings show a different relaxation behavior between surface and core. Complementary investigations revealed that recrystallization occurs at a higher temperature in the core compared to the surface. The surface of cold rolled rings and machined rings present a similar behavior: recovery processes induce a decrease of residual stresses at temperatures up to 500 °C and recrystallization starts above 500 °C which causes a complete residual stress relaxation. In the core of cold rolled rings, recovery processes are still active until 600 °C where recrystallization begins. However, residual stresses in the core are already completely relaxed at 600 °C.     

X90高强度管线钢预精焊冷裂纹形貌及成因

采用力学测试、组织分析、扫描电镜和能谱分析的方法,研究了X90高强度管线钢预精焊的焊接裂纹形貌,并分析了裂纹形成原因.结果表明,X90螺旋焊钢管内焊缝上的横向裂纹为冷裂纹,裂纹在焊缝组织中呈穿晶扩展或沿晶界扩展.X90含有较多的Mn,Cr,Mo,Ni,Cu等合金元素,强度高,导致内焊缝的焊接残余应力高于裂纹的临界应力.内焊道维氏硬度比外焊道的高,且焊缝两侧的硬度分布极不对称,造成了内焊道附近的应力集中和分布不平衡.内外焊缝重合区域的扩散氢不易逸出,其含量较高,在气孔、夹渣等“陷阱”处聚集,导致裂纹产生和断口上大量氢白点形成.焊缝一次结晶所形成的连续细长的树枝晶晶界为裂纹扩展提供了“通道”.