Determination of Vickers indentation fracture toughness of boronised alloyed ductile iron

In the present study, copper (Cu), nickel (Ni), and molybdenum (Mo)-alloyed ductile iron was pack boronised at 800–850°C for 3–6?h and subsequently the microhardness and the microstructures of boride layers under different process parameters were investigated in detail. Further, Vickers indentation fracture toughness tests were executed on borided surfaces under 200?g load. The fracture toughness of borided layers was estimated separately by a series of equations and the half-length of corner cracks and the half diagonals of Vickers indents were used as variables. Generally, the values of the obtained fracture toughness were found to be higher than those of previous studies. It was found that thinner boride layers were formed at lower boronising temperatures. The highest toughness value and the thickest boride layer were obtained in the sample boronised at 850°C for 6?h.     

Ball indentation tests for a Zr-based bulk metallic glass

Zr_52.5Ti₅Cu_17.9Ni_14.6Al₁₀ bulk metallic glass was characterized using ball indentation tests. Comparison of the data with the expanding cavity model revealed that the deformation is pressure insensitive for compressive loading. The plastic flow curves obtained from indentation tests showed perfectly plastic response and no strain rate sensitivity up to 15% strain.     

Interface fracture toughness and fracture mechanisms of thermal barrier coatings investigated by indentation test and acoustic emission technique

Interface fracture toughness and fracture mechanisms of plasma-/sprayed thermal barrier coatings (TBCs) were investigated by interfacial indentation test (IIT) in combination with acoustic emission (AE) measurement. Critical load and AE energy were employed to calculate interface fracture toughness. The critical point at which crack appears at the interface was determined by the IIT. AE signals produced during total indentation test not only are used to investigate the interface cracking behavior by Fast Fourier Transform (FFT) and wavelet transforms but also supply the mechanical information. The result shows that the AE signals associated with coating plastic deformation during indentation are of a more continuous type with a lower characteristic frequency content (30-60 kHz), whereas the instantaneous relaxation associated with interface crack initiation produces burst type AE signals with a characteristic frequency in the range 70-200 kHz. The AE signals energy is concentrated on different scales for the coating plastic deformation, interface crack initiation and interface crack propagation. Interface fracture toughness calculated by AE energy was 1.19 MPam_1/2 close to 1.58 MPam_1/2 calculated by critical load. It indicates that the acoustic emission energy is suitable to reflect the interface fracture toughness.     

压痕应变法测量焊缝应力时的近似修正方法

压痕应变法作为近年来出现并已得到工程应用的一种新型残余应力测量技术,正在受到日益重视.目前通过应变增量计算残余应力的方法仍然是通过事先试验标定,测量超强或低强匹配焊缝中的残余应力时采用的仍然是母材的标定系数,因而会带来严重误差.首先对压痕周围物理变形场进行了相应分析,继而提出一种计算焊缝残余应力的近似修正方法,从而使焊缝应力的测量精度大大提高.     

Evaluation of microhardness,fracture toughness and residual stress in a thermal barrier coating system: A modified Vickers indentation technique

The evolution of microhardness, fracture toughness and residual stress of an air plasma-sprayed thermal barrier coating system under thermal cycles was investigated by a modified Vickers indentation instrument coupled with three kinds of indentation models. The results show that fracture toughness on the top coating surface after thermal cycles changes from 0.64 to 3.67 MPa m^1/2, and the corresponding residual stress near the indented region varies from − 36.8 to − 243 MPa. For the interface region of coating and bond coat, fracture toughness in the coating close to interface ranges from 0.11 to 0.81 MPa m^1/2, and residual stress varies from − 5 to − 30 MPa, which are consistent with available data. For the lateral region of coating, fracture toughness and residual stress display strong gradient characteristics along the thickness direction due to the special layered structure.     

烧结NdFeB永磁合金的断裂韧性

用Zwick万能实验机测量了烧结NdFeB永磁合金样品的三点弯曲强度、断裂韧性KIC及弹性模量E。在三点弯曲试验中测得塑变功为0，而断裂功与最大消耗功相等，表明烧结NdFeB合金具有极大的缺口敏感性。缺口敏感的脆性材料用单边切口粱法（SENB）测量KIC时要求较高的抛光精度，以消除表面划痕的影响，比较而言，压痕法测量KIC简便迅速。但由于所用NdFeB合金为烧结复相材料，其微观结构的不均匀性使实验数据较为分散。本研究借助Palmqvist裂纹系统半椭圆裂纹模型HV-KIC的计算公式，采用开微缺口的单边缺口粱试样的KIC和压痕硬度及系列压痕裂纹参数，经回归分析确定了该公式中的经验常数，使之能够较为准确地表征烧结NdFeB永磁合金的断裂韧性。     

热处理工艺对Fe-Co-Zr-Mo-W-B大块非晶合金断裂韧度的影响

采用电弧熔炼母合金、感应加热熔化、铜模吸铸工艺,制备了厚度为1mm的板状Fe-Co-Zr-Mo-W-B系Fe基大块非晶合金,铸态试样表面及断口光亮,具有典型的金属光泽,但脆性严重。本文采用压痕试验法研究了热处理工艺对铸态Fe基大块非晶合金脆性的影响。结果表明,合适的退火工艺可使Fe基大块非晶合金的断裂韧度提高到铸态的260％。     

渗硼层脆性判据K的物理本质

从实验和理论上对显微硬度压痕结合声发射测量渗硼层脆性的合理性及其脆性判据Ｋ的物理意义进行了讨论。Ｋ值可以反映渗硼层显微压痕裂纹长度随负荷增加的变化率，因而可以表征渗硼层的脆性。根据断裂力学可以导出入与Ｇ＿（ＩＣ）之间存在如下关系：Ｋ＝β（Ｇ＿Ｉ－Ｇ＿（ＩＣ））。Ｋ值间接反映了渗硼层的断裂韧性，可以作为定量评价渗硼层本质脆性的力学参量。     

提高高铬白口铸铁磨球冲击抗力的技术关键

当高铬白口铸铁含铬量为18%～28%,Cr/C值是8￣9,铸铁的显微组织是回火马氏体 少量残余奥氏体(<5%) M7C3碳化物,则磨球具有高的冲击韧性和断裂韧性K1C,具有高的冲击抗力,表现出低的冲击剥落量。     

深冷处理对TiN涂层硬质合金力学性能的影响

采用电弧离子镀技术在YW2硬质合金基体上沉积了厚度为2μm的TiN涂层,对所获得的TiN/YW2体系进行了-196℃下30 h的深冷处理。采用X射线衍射仪(XRD)和显微硬度仪分别对深冷前后TiN涂层的相结构和硬度进行了检测,利用洛氏硬度仪采用压痕法研究了深冷处理前后YW2基体和TiN/YW2体系压痕形貌的变化,借助金相显微镜和扫描电镜(SEM)研究了基体显微组织及其对体系断裂韧性、界面结合状况的影响。结果表明:深冷处理后涂层中应力诱导晶粒扭转导致的TiN(111)面择优取向,使体系的硬度得到了提高。基体上压痕径向放射性裂纹密度明显降低,TiN涂层沿压痕周向的块状剥离得到缓解。深冷处理后弥散分布的颗粒状γ相显著减少或消失、孔隙率降低,组织变得更加致密,加之深冷处理过程中裂纹源的弥合,提高了YW2基体和TiN/YW2体系的断裂韧性和界面结合强度。     

Evaluation of interfacial strength by an instrumented indentation method and its application to an actual TBC vane

The thermal fatigue behaviour of an air plasma sprayed thermal barrier coating was investigated. And also the interfacial strengths of thermal barrier coated specimens subjected to thermal fatigue, as well as a retired TBC vane were also evaluated by means of an instrumented indentation machine. The results indicated that, (1) the TGO grew at the interface during thermal fatigue cycle as a function of the exposure time at elevated temperature; (2) the microcracks were initiated in the top coating and at the...     

Interfacial indentation test of FeB/Fe2B coatings

The present study uses interfacial indentation testing to estimate the adhesion of the FeB/Fe₂B coating formed on the surface of borided AISI 316 steel. This technique creates and propagates a crack along the FeB/Fe₂B interface and defines the apparent fracture toughness, which can then be related to the adhesion and mechanical support of the aforementioned interface. The boriding process was performed on the surface of AISI 316 steel by means of the powder-pack method at temperatures of 1123, 1173, 1223 and 1273 K with 2, 4, 6, 8 and 10 h for each temperature. The Young's modulus for each surface layer was obtained by Knoop microindentation at a constant indentation load. Vickers microindentation fracture technique was used to generate microcracks at the FeB/Fe₂B interface with varying indentation loads. The applied load, Young's modulus, hardness, and lateral crack lengths generated from the corners of the indentations, along with the depth of the FeB layer, were used to determine the apparent fracture toughness and adhesion of the FeB/Fe₂B interface. The apparent fracture toughness of the FeB/Fe₂B interface varied between 3.56 and 4.45 MPa . Finally, the intensity of residual stress at the FeB/Fe₂B interface was estimated as a function of the FeB layer thickness.     

高分子薄膜润滑在板料拉深中的应用研究与发展趋势

介绍了高分子薄膜润滑在板料拉深中的应用研究与发展趋势,分别从高分子摩擦润滑的机理、板料成形中高分子薄膜的润滑工艺以及高分子润滑材料的摩擦学研究3个方面概述了目前高分子薄膜润滑的研究及应用现状、高分子润滑剂的润滑特点,简述了高强度钢板拉深成形中存在的问题和高强度钢板成形时采用高分子薄膜进行润滑会获得良好的成形性能,并指出高分子薄膜润滑存在的问题和发展趋势。     

中厚板炉底辊压痕缺陷原因分析及控制方法

针对影响热处理钢板表面质量的炉底辊压痕缺陷问题，分析了其主要影响因素，如炉内氧化气氛、钢板规格、高温工艺以及钢板表面抛丸质量和表面粗糙等对缺陷产生的影响。通过加强炉底辊质量把关、对钢板进行入炉检查以及对抛丸质量和炉内气氛严格控制，同时对生产计划安排和洗炉制度进行优化，使炉底辊压痕缺陷得到明显改善和控制，月均压痕量由500 t降至100 t。     

中厚板炉底辊压痕缺陷原因分析及控制方法

针对影响热处理钢板表面质量的炉底辊压痕缺陷问题，分析了其主要影响因素，如炉内氧化气氛、钢板规格、高温工艺以及钢板表面抛丸质量和表面粗糙等对缺陷产生的影响。通过加强炉底辊质量把关、对钢板进行入炉检查以及对抛丸质量和炉内气氛严格控制，同时对生产计划安排和洗炉制度进行优化，使炉底辊压痕缺陷得到明显改善和控制，月均压痕量由500 t降至100 t。     

Fracture toughness of thermal spray ceramic coatings determined by the indentation technique

The indentation technique for determining material toughness is applied to spinel and yttria-stabilized zirconia plasma-sprayed coatings in this investigation. Fracture toughness of the coatings ranged from 1.9 to 3.4 MPa√m for spinel and 2.0 to 3.3 MPa√m for yttria-stabilized zirconia. These results are in good agreement with those obtained by other experimenters for bulk materials.     

Response of ductile metal sheet parameters to the cone angle of indenting conical tool and fracture toughness evaluation

The indentation and perforation of ductile metal sheet with a conical tool is accompanied by elastoplastic bending, stretching, plastic flow, and crack initiation and propagation. This ultimately results in material fracture in the form of petals. It has been observed that the perforation process is dependent upon the angle of the conical tool. Fracture toughness, crack initiation, work input before and after crack initiation, number of petals, and sheet and petal bending angles all depend on the tool angle. Crack initiation has resulted at minimum tool displacement for a tool angle α=45°, while minimum work input before and after the crack initiation is observed when the tool has an angle α=35°. The optimum range of tool angles for the indentation process is α=22.5 to 50°. In this range, the aluminum sheets showed minimum fracture toughness as well as minimum work input to overcome the offered resistance.     

Failure Mechanism for Thermal Fatigue of Thermal Barrier Coating Systems

Thick thermal barrier coatings (TBCs), consisting of a CoNiCrAlY bond coat and yttria-partially stabilized zirconia top coat with different porosity values, were produced by air plasma spray (APS). The thermal fatigue resistance limit of the TBCs was tested by furnace cycling tests (FCT) according to the specifications of an original equipment manufacturer (OEM). The morphology, residual stresses, and micromechanical properties (microhardness, indentation fracture toughness) of the TBC systems before and after FCT were analyzed. The thermal fatigue resistance increases with the amount of porosity in the top coat. The compressive in-plane stresses increase in the TBC systems after thermal cycling; nevertheless the increasing rate has a trend contrary to the porosity level of top coat. The data suggest that the spallation happens at the TGO/top coat interface. The failure mechanism of thick TBCs was found to be similar to that of conventional thin TBC systems made by APS.     

球形压痕法评价(Ti,Nb)N膜层断裂性能

采用球形压痕试验，在高速钢基体上对电弧离子镀工艺沉积制备的(TixNb)N膜层断裂性能进行评价。在600N载荷下，在压痕的周围只产生径向裂纹；统计分析压痕周围产生的裂纹，采用裂纹密度函数β，对膜层的断裂性能进行了分析。结果表明：(TixNb)N均质膜层在显微硬度提高的同时，裂纹密度β增加，膜层的脆性增大，断裂韧度下降。TixNb1-xN梯度膜具有较高膜层显微硬度，仍然具有较好的断裂韧度，预渗氮处理的膜层裂纹密度较小，膜层的断裂韧度最好。采用裂纹密度函数卢统计分析，通过对(TixNb)N膜层压痕试验，可以很好的定量和半定量地比较膜层的断裂性能。     

MoSi_2复合材料断裂韧性的测量及评价

对压痕法和单边切口梁法所测MoSi2 基复合材料的断裂韧性作了研究和分析 ,提出了压痕法测量MoSi2 基复合材料断裂韧性的计算修正式。结果表明 :单边切口梁法的测量结果随试样切口宽度的增加而增大 ,压痕法测量的结果随计算式和试验载荷的不同而异。使用上述修正式将缩小压痕法与SENB法的测量偏差