CrMoV和CrNi堆焊涂层耐泥沙冲蚀磨损性能研究

利用自制的冲蚀磨损试验装置,对水力机械过流部件堆焊修复中常用的CrMoV和CrNi合金堆焊涂层进行了液固两相流冲蚀磨损性能研究。结果表明:在低角度冲蚀磨损条件下,CrMoV合金堆焊涂层表现出优于CrNi合金堆焊涂层的耐泥沙冲蚀磨损性能,堆焊层硬度是耐泥沙冲蚀磨损的主要因素;在高角度冲蚀磨损条件下,CrNi合金堆焊涂层表现出比CrMoV合金堆焊涂层更好的耐泥沙冲蚀磨损性能,堆焊层组织的断裂韧性是主要因素;冲蚀磨损量随冲蚀速率增加而显著增加,冲蚀磨损率取决于冲蚀磨粒的能量。     

Study of indentation induced cracks in MoSi2-reaction bonded SiC ceramics

MoSi₂-RBSC composite samples were prepared by infiltration of Si-2 at.% Mo melt into a preform of commercial SiC and petroleum coke powder. The infiltrated sample had a density > 92% of the theoretical density (TD) and microstructurally contained SiC, MoSi₂, residual Si and unreacted C. The material was tested for indentation fracture toughness at room temperature with a Vicker’s indenter andK _IC was found to be 4.42 MPa√m which is around 39% higher than the conventional RBSC material. Enhancement in indentation fracture toughness is explained in terms of bowing of propagating cracks through MoSi₂/SiC interface which is under high thermal stress arising from the thermal expansion mismatch between MoSi₂ and SiC.     

Erosion Resistance of Stellite Alloys under Solid-Particle Impact

Selected Stellite alloys, which are currently or potentially employed in an environment involving erosion, are studied under solid-particle erosion test. These alloys include high-carbon Co-Cr-W system and low-carbon Co-Cr-Mo system, Two particle impact velocities （84 m/s and 98 m/s） and two impingement angles （30° and 90°） are used in the test. It is shown that Stellite alloys are more resistant to erosion at 90° impingement angle than at 30° impingement angle and the weight losses of Stellite alloys increase with the particle impact velocity. The erosion resistance of Stellite alloys is controlled mainly by their carbon content, but tungsten and molybdenum contents also play an important role in the erosion resistance of these alloys, because these elements determine the volume fractions of carbides and intermetallic compounds in the alloys. The eroded surfaces are analyzed using SEM to further understand the erosion test results.     

结构陶瓷的空蚀性研究

利用转盘装置测量了ZrO2、Si3N4和Al2O3／Ti(NC)等陶瓷材料受到水的空蚀破坏的体积损失,通过SEM观察和XRD分析,探讨了微观结构和抗空蚀性能的关系。     

舰船结构钢的夏比冲击韧性与断口形貌

论述了从夏比冲击韧性分解出来的断裂扩展功与断口形貌的关系，指出冶金因素对夏比冲击韧性α＿ｋ值和扩展功的影响不完全是一致的，提出采用α＿ｋ，值和断口纤维率作为韧性指标的互补性，建议在我国的舰船结构钢韧性指标中增加断口纤维率的要求。     

放电等离子烧结法制备牙科陶瓷的研究

采用放电等离子烧结(SPS)法制备长石类牙科陶瓷,研究了烧结工艺对其性能的影响。结果表明,在压力30MPa,烧结升温速度100℃/min,烧结温度1120-1300℃下,SPS能够实现长石瓷的高密度烧结,断裂韧性达到1.4MPa·m1/2以上。     

Q500钢焊接接头断裂韧性K_C与冲击功KV_2的相关性统计规律

采用深缺口宽板拉伸试验测定了4种板厚规格(20 mm、32 mm、40 mm和60 mm)Q500钢焊接接头在不同温度下的断裂韧性KC,对32组断裂韧性值及对应试验温度下的冲击功KV2值的相关性进行了统计分析,结果表明,断裂韧性KC与KV2/t近似呈线性关系,其拟合方程为KC=80.6+7.23·KV2/t。     

Workability assessment of structural steels of power plant units in hydrogen environments

For estimation of hydrogen influence on the workability of high-stressed parts of power plant unit equipment it is necessary to use the crack growth resistance parameters. The new 18Mn-18Cr steel has higher resistance to hydrogen embrittlement and longer residual life time in hydrogen, than the traditional 8Mn-8Ni-4Cr steel. __________ Translated from Problemy Prochnosti, No. 1, pp. 69–75, January–February, 2009.     

Effect of Laves phase on the toughness of P92 weld metals

In this investigation, Laves phase was found to gradually precipitate from the tempered martensitic matrix of the two P92 weld metals (WMs) during the aging treatment. The particle size of Laves phase in the two WMs was ranged from 0.18 to 0.24 μm and was larger than the M₂₃C₆ particle size (ranged from 0.09 to 0.13 μm). The dislocation density of the two WMs was stable during aging. The hardness of the two WMs was stable during aging treatment, as the loss of solid solution strengthening was continuously compensated by the precipitation strengthening of Laves phase. The impact toughness of the two WMs declined gradually as the extending of aging time. The crack initiation zone and shear lip zone of the fracture surface were ductile fracture mode which consumed more fracture energy during impacting. The generation of Laves phase narrowed the crack initiation zone and shear lip zone and contributed to the decline of ductile fracture area percentage of aged WMs. The smaller ductile fracture area percentage contributed to the toughness reduction of aged WMs.     

Erosion mechanisms of aluminium nitride ceramics at different impact angles

In this paper, erosion wear behaviour of aluminium nitride (AlN) ceramics is studied. The influence of particle hardness and shape on erosion of the AlN surface is examined. The effect of varying the impingement angle on the weight loss and the roughness parameters of AlN ceramics testing sample is also determined. Therefore, erosive wear behaviour of AlN ceramics was investigated using SiC and SiO₂ particles as erodents, at following impact angles: 30°, 45°, 60°, 75° and 90°. Scanning electron microscopy (SEM) was used to analyze the eroded surfaces in order to determine erosion mechanisms. The roughness parameters (R_a, R_z and R_max), before and after erosion with SiO₂ and SiC particles at 30° and 90° angles of impingement, respectively, were determined using a profilometer. It was found that the impact angle is influencing the erosion wear of the AlN ceramics and maximum erosion takes place at impact angle of 90°. The results indicate that hard, angular SiC particles cause more damage than softer, more rounded SiO₂ particles.     

碳基材料超高速粒子侵蚀的数值模拟

应用动力学理论建立了碳基材料超高速粒子侵蚀的数学模型。在模型中引入了表征材料抵抗侵蚀破坏能力的参数: 冲击破坏侵蚀能和剪切破坏侵蚀能。通过定义多重碰撞修正因子β, 给出了多粒子侵蚀材料体积损失的理论计算公式。计算了石墨和C/ C 靶材在Al₂O₃粒子撞击下, 体积损失比随粒子入射角及入射速度的变化规律。结果表明, 脆性碳基材料在超高速粒子撞击作用下, 冲击破坏与剪切破坏同时发生, 冲击破坏在材料体积损失中起主导作用。计算结果与已有的实验值吻合较好。      

Strength of a half space weakened by a plane circular crack

The methods of the mechanics of brittle fracture and the theory of generalized cleavage fracture are used for the approximate solution of the problem of strength of a half space weakened by a plane circular crack. A simplified computational scheme is proposed for the evaluation of the fracture load in the case of free (tensile) fracture. The results of theoretical investigations are experimentally confirmed by testing concrete specimens. __________ Translated from Problemy Prochnosti, No. 6, pp. 122–132, November–December, 2006.     

Influence of carbides morphology on fracture toughness of cast steel G200CrMoNi4-3-3

We analyze the influence of small modification of chemical composition of G200CrMoNi4-3-3 cast steel on the morphology of carbides and on material crack resistance. Using the Termo-Calc software the volume fraction of carbide phase was determined and the results correlated with microstructure observations. Crack resistance of cast steel was determined using SENB specimens and finding critical values of stress intensity factor K_Q. Metallographic and fractographic observations of fracture surfaces allowed identifying the mechanism of cracking. __________ Translated from Problemy Prochnosti, No. 1, pp. 137–140, January–February, 2008.     

复合材料层合板低速冲击损伤容限的改进方法和影响因素

依据笔者在这方面的研究和前人的工作，以及现有各种改进炭纤维增强树脂基复合材料冲击性能的方法，分析和总结了复合材料层合结构冲击损伤以及损伤容限，其中主要是冲击后压缩强度的重要影响因素，并且讨论了这些因素的作用。     

Fatigue fracture toughness of metals

The paper considers the peculiarities of fatigue crack propagation and final fracture of metals under cyclic loading. It is shown that the value of the fatigue fracture toughness of steels in an embrittled state is appreciably lower than that of the fracture toughness under static loading. A model of the transition from stable to unstable fatigue crack propagation is justified.     

冲击能量对ESSO试验结果的影响

对90mm厚EH47船用钢板进行了不同冲击能量下的梯度温度型ESSO试验以分析冲击能量对试验结果的影响.结果表明,采用下限冲击能量测得的-10℃止裂韧性值与双重拉伸试验所测值基本一致,但根据WES:2815-2014规范确定的上限冲击能量测得的止裂韧性值明显低于前两者测得的结果,建议后续在ESSO试验中针对90mm厚钢板选用冲击能量下限值进行试验.     

锰、铜含量对锌铝合金组织与性能的影响

研究了不同含量的锰和铜对锌铝合金的组织与力学性能的影响。结果表明：锰和铜含量较低时,对合金的力学性能无显著影响;随着锰和铜含量的升高,合金的硬度大幅提高,冲击韧度基本不变。     

On the fracture toughness anisotropy of mechanically poled ferroelectric ceramics

In this paper an incremental constitutive theory for the deformation due to switching in ferroelectrics is applied to predict the fracture toughness anisotropy in these materials after mechanical poling. Mechanical poling of an initially unpoled specimen differs from electrical poling in that only mechanical stresses are applied to the material. Therefore, no electrical polarization can develop. After mechanical poling, for example by a uniaxial applied stress, the fracture toughness of a ferroelectric ceramic for cracks running parallel or orthogonal to the poling direction will differ. Finite element computations of the steady crack growth process have been carried out to quantify these differences. Results are generated for a range of constitutive properties for three crack growth directions with respect to the initial mechanical poling direction. The results are discussed in relation to available experimental data and to the toughness anisotropy due to electrical poling.     

Erosion of polymers and polymer composites surfaces by particles

Surface erosion due to solid particle impact is a major concern in engineering applications of handling solid-particulate flow. A semi-empirical model is developed for numerical erosion simulation of polymers and polymer composites. The novelty of the developed model is the correct capturing of the angle of maximum erosion for different erosion modes of polymeric materials and relating it to measurable mechanical properties of the target materials. The model incorporates both the material removal due to elastic–plastic collision of the particles at oblique and normal impact angles. The oblique impact model is derived for ploughing and fracture governed mechanisms of material removal. A simplified correlation is used to consider the relative effect of each mechanism on the total erosion at oblique impact angles. The model indicates the variation in velocity exponent to the mechanism of material removal. The theoretically derived model for single-particle impact is correlated to the available experimental results of multi-particle impacts through the empirical coefficients. The predictions are in good agreement with the extensive literature data for polymers and polymer composites. Further, to propose a single model of erosion for polymer and its composite, the relationship between the empirical coefficients in the developed model and the target material properties is established.