Cavitation erosion of NiAl-bronze layers generated by friction surfacing

Friction surfacing is a solid-state process, which allows deposition welding at temperatures below the melting range. For this investigation coating layers of NiAl-bronze were deposited by friction surfacing on self-mating substrates, followed by microstructural characterisation. Further, cavitation tests were performed in order to investigate wear resistance. Cavitation erosion mechanisms were analysed by means of optical and electron microscopy. All coatings show incubation periods about twice as long as those of the substrate material, while their average rate of material loss is about one half of that of the substrate. The differences in cavitation erosion resistance are due to more ductile behaviour of the coatings, as well as corrosion increasing the wear of the as-cast material.     

Relations between cavitation erosion resistance of materials and their fatigue strength under random loading

The paper contains results of tests on fatigue strength under uniaxial random loading and cavitation erosion resistance for three steels: 10HNAP, 18G2A and 15G2ANb. The obtained fatigue and cavitation characteristics were used for determination of relations between these two phenomena. From the analysis it appears that there is correlation between fatigue strength of the material under random loading and its cavitation erosion resistance. It has been shown that fatigue tests under random loading and tests on cavitation erosion of 10HNAP, 18G2A and 15G2ANb steels may be described with a mathematical model of the same type. It has been also found that there is a linear relation, in the dual logarithmic system, between cavitation erosion resistance of the steels tested and their fatigue strength under random tension—compression with zero mean value.     

Nonlinear cavitation erosion of stainless steel in mercury versus applied power

The cavitation erosion rate for 316 stainless steel in mercury was found to increase in a nonlinear fashion with the maximum applied power. In addition, the incremental increase in erosion was observed to decrease with increased power in water, yet increased six to seven times when mercury was used as the cavitating fluid. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effect of liquid metal composition and hydrodynamic parameters on cavitation erosion

Cavitation erosion testing machine for low-temperature melting alloy liquid was developed by using a vibratory apparatus. The erosion tests of SUS304 were carried out in three kinds of lead–bismuth and deionized water. We defined a relative temperature as the percentage between freezing and boiling points. At relative temperature at 14 °C, the erosion rate is 10–12 times in various lead–bismuth alloys, and 2–5 times in sodium, as compared with that in deionized water. When SUS304 was exposed to a cavitation in PbBi, the surface was work hardened 20% harder compared with original surface. In deionized water, SUS304 was work hardened by 5%. Therefore, we can conclude that larger collapse pressure can be estimated to act on the specimen surface in lead–bismuth, as compared with that in water.We discussed the effect of hydrodynamic properties on cavitation erosion in a flowing system. It is considered that the erosion rate in sodium is in proportion to 1st to 6th power of flow velocity similarly to that in mercury. The incipient cavitation number is approximately unity irrespective of test liquids. Furthermore, the relation between MDER and cavitation number is expressed as power low of function with an exponent of 2.5.     

Cavitation erosion resistance of stellite alloy weld overlays

Stellite alloys have excellent cavitation erosion resistance and are often used for liquid machinery, but the erosion properties of various stellite alloys have not been evaluated by a standard method. In this study, we evaluate the erosion resistance for various stellite alloy weld overlays of ST6 and ST21 in a vibrating method and in a cavitating liquid jet method. The grain size of the Co matrix affects the cavitation erosion resistance of stellite alloy weld overlays of ST6. The erosion rate of the maximum rate stage of stellite weld overlay alloys of ST6-1, ST6-2 and ST6-3 were found to be about 1/13 to 1/7 times that of SUS304. Moreover, we clarified the cavitation erosion mechanism of SUS304 and ST6 by scanning electron microscopy. Furthermore, by comparing the erosion behavior in a cavitating liquid jet method with that in a vibratory method, it was found that the erosion rate of the cavitating jet method and the vibratory method have a good correlation.     

SUS304不锈钢ELID镜面磨削正交化实验研究

SUS304不锈钢具有高耐腐耐磨性和良好的综合性能而被广泛应用,但其高韧性和低导热性使传统的SUS304不锈钢磨削或车削工艺存在一定困难。在线电解修整ELID(Electrolytic in-process dressing)磨削技术能有效地用于SUS304不锈钢镜面磨削加工。本文主要对SUS304不锈钢进行ELID镜面磨削正交化实验研究以获得合理的工艺参数。首先利用#325砂轮进行7个影响因素2水平的正交磨削实验,获得初步的优化参数,然后利用#1200砂轮进行3个影响因素2水平的正交镜面磨削实验。通过改变削件砂轮转速、X和Y平台移动速度、进给率和ELID电源件等各种磨削条件,获得优化后的磨削工艺参数,进行了相应的磨削验证,并讨论了工艺参数对磨削特性的影响。研究了不同砂轮磨粒对表面粗糙度的影响,使用#8000金刚石砂轮对SUS304不锈钢镜面磨削,获得表面粗糙度Ra=3.6 nm。     

Influence of temperature on erosion by a cavitating liquid jet

The influence of water temperature on cavitation erosion has previously been studied using a vibratory apparatus, but no researches have been conducted at a constant cavitation number in flow condition. This study deals with the influence of the water temperature on cavitation erosion using a cavitating jet apparatus. The optimum stand-off distance at 25 °C was 11, 15, 21 and 25 mm at cavitation number of σ = 0.03, 0.025, 0.02 and 0.015, respectively, and was almost the same as that of a guideline in the ASTM G134 standard. The optimum stand-off distance at 75 °C is similar to that at 25 °C. The erosion rate increases with the liquid temperature and reaches a peak, followed by a decrease. The relative temperature was defined as 0 °C for freezing temperature and 100 °C for boiling temperature of pressurized water. The peak appears at the approximate average of freezing and boiling relative temperatures. The erosion rate increases by 1%/ °C between 5 and 45 °C of relative temperatures, and decreases by 2%/ °C between 45 and 80 °C.     

Q355NE+SUS304异种金属焊接接头组织与腐蚀疲劳性能研究

以Q355NE+SUS304异种金属焊接接头为研究对象,对其显微组织、3.5％NaCl+0.5％Na2SO4(质量分数),PH=5溶液腐蚀疲劳和腐蚀疲劳断裂特征进行了研究,分析了异种金属焊接接头腐蚀疲劳性能和断裂过程.结果表明:试验级腐蚀疲劳极限在170MPa左右,腐蚀疲劳裂纹起源于Q355NE侧的热影响区,逐渐扩展最...     

Cavitation erosion resistance of Cr–N coating deposited on stainless steel

Results of investigation on cavitation-erosion resistance of Cr–N coating deposited on stainless steel X6CrNiTi18-10 (1H18N9T) by means of the cathodic-arc method are presented. The evaluation of Cr–N coating resistance to cavitation erosion is based on the investigation performed in a cavitation tunnel with a slot cavitator and tap water as a medium. The investigation was performed at variable-cavitation intensity and the estimated cavitation resistance parameters of coatings were the incubation period of damage and the instantaneous erosion rate after exposure of specified duration. It has been confirmed that the incubation period of the Cr–N coating damage is approximately 50% longer than that of the uncoated X6CrNiTi18-10 steel, and the instantaneous erosion rate after exposure of specified duration is comparable in both cases. The scanning microscope analysis indicates that the damage of Cr–N coating is due mainly to its delamination, while the erosion of deeper parts of the coating is of minor importance. The character of the coating and substrate damage in multiple locations indicates that the hard coating microparticles torn-off during the cavitation bubbles implosion hit against the coating and the revealed areas of substrate. As a result, the coating and especially the substrate of relatively low hardness are subject to cavitation erosion and to solid particle erosion with the hard torn-off microparticles of coating. The results of the investigation and the analysis indicate that the factors mainly responsible for a long incubation period and low cavitation erosion rate of the steel substrate/hard coating systems are the gained high hardness of substrate and high level of coating adhesion.     

SUS304亚稳奥氏体不锈钢在耦合摩擦和变形条件下的磨损行为研究

在自制的耦合摩擦和变形的试验机上初步研究了SUS304亚稳奥氏体不锈钢带的磨损变形行为,分析了在耦合摩擦和变形条件下的形变量、磨痕表面的马氏体转变以及磨痕形貌与试验条件的关系。结果表明:研制的试验机实现了SUS304亚稳奥氏体不锈钢带的摩擦和塑性变形的耦合行为;不仅带试样摩擦表面的形貌随正压力增加变化明显,而且其形变量和诱发转变的马氏体量均增大,但马氏体量增加对SUS304奥氏体不锈钢的磨损无明显影响。     

The cavitation erosion damage process of dynamically loaded journal bearings

The cavitation damage model was built using finite element analysis software MSC.Marc. This paper attempted to numerically analyze the action process based on damage mechanics when a jet created by bubble collapse acted on the bearing surface in the process of cavitation erosion. The numerical results show that the values of equivalent plastic strain and void volume fraction increase with time. The values of damage scalar are higher on the bearing surface and subsurface, and decrease when it approaches the interface of overlay and nickel layer. The strain history and damage evolvement of bearing material acted on by jet impact load can be calculated efficiently using the proposed method, which develops a new method of analyzing cavitation erosion failure of the bearing surface. __________ Translated from Journal of Shanghai Jiaotong University, 2005, 39(7) (in Chinese)     

304H奥氏体不锈钢丙烷脱氢反应器的焊后热处理

简要介绍了304H奥氏体不锈钢丙烷脱氢(PDH)反应器的焊后热处理工艺,针对反应器的设计结构以及材料本身的特性,通过热应力分析,制定了合理的炉内热处理工艺;参照WRC-452制定了合理的环缝局部热处理工艺;同时通过多点温度采集仪对温度的记录,有效减少了工件的温差,解决了304H整体容器高温焊后热处理的技术难题,为今后同类设备的制造提供可行性经验。     

High temperature erosion of Ti(Mo)C–Ni cermets

The resistance of Ti(Mo)C–Ni cermets of different binder content to solid particle erosion was evaluated at 25, 350 and 650 °C. The elevated temperature erosion of cermets containing 40, 50, 60, 70 and 80 wt.% of titanium carbides and produced from the powder of initially different ratios of Ni to Mo were tested with the help of specially designed centrifugal particle accelerator using silica as the abrasive. Erosion rate was related to both microstructure developed during sintering and materials removal mechanisms operating at the test conditions (impact angle of particles jet was 30° and 90° and velocity was 50 ms⁻¹). The erosion rate decreases with the increase of TiC and Mo contents in the composite. At 650 °C the process of tribo-oxidation affected the material performance to a great extent. The morphology of the worn surface was analyzed with SEM to determine the erosion mechanisms.     

Characterization of erosion of gas pipelines by dry sand

In oil and gas industry, the economic considerations determine the selection of low cost materials, in general, carbon steel, for pipelines. However, another type of deformation that is not well understood is its erosion resistance. The objective of this study was to investigate the factors affecting the erosion of carbon steel in a dry sand stream. In this work, a laboratory built test rig was used to erode representative carbon steel plates with accelerated sand streams. The results revealed that the normal incidence sand stream of larger particles and higher impact velocities causes more erosion of the carbon steel. The highest erosion rate of 6.75 ± 0.16 was predicted at an impact angle of 90°, which was three times higher than the erosion rate at impact angle of 30°. Similarly, the erosion caused by the smaller particles was not as severe as the larger particles. The cross-section profiles revealed that the crater depth was increased from 7° to 32.8° with an increase in sand size from 200 µm to 600 µm. The deepest crater of 32.8° was induced by the largest sand size of 600 µm.     

Erosion of metals using angular silicon carbide particles

ABSTRACT

In this work, erosion tests conducted to evaluate the resistance of two materials, Metal Babbitt Grade 7 and AISI T1 against SiC particles. The erosion rates of these two metals compared with those obtained using AISI D2 steel in a previous work with similar testing conditions. Metal Babbitt and AISI T1 steel selected due to their high ductility and strength, respectively. A test rig similar to that shown in ASTM G76-95 standard used to perform the tests. Silicon carbide particles had a particle size between 350–450 µm. Tests carried out using different impact angles, 30°, 45°, 60° and 90° with a particle velocity of 24 ± 2 m/s and the abrasive flow rate was 0.7 ± 0.5 g/min. SEM photographs used to identify the wear mechanisms on the Babbitt and T1 steel and also obtained cross-section images of the wear scars on metal Babbitt to measure their depth.     

Study of solid particle erosion on AISI D2 using angular silicon carbide and steel round grit particles

Abstract

In this study, the performance of AISI D2 steel subjected to solid particle erosion tests was analysed. This material has applications for tools and dies for blanking, wood milling cutters, cold-extruding and other operations requiring high compressive strength and excellent wear resistance. The erosion tests performed by using a rig developed according to some parameters of the ASTM G76-95 standard. Two abrasive were used, angular silicon carbide (SiC) and steel round grit, both, with a particle size of 400–420 μm. This allowed comparing the erosion severity of each abrasive particle. The tests were conducted using four different incident angles 30, 45, 60 and 90° with a particle velocity of 24±2 m s^?1 and a flow rate of 21±2·5 g min^?1 for silicon carbide and 48·5±3·5 g min^?1 for the steel round grit. The exposure testing time was 10 min. Subsequently, the surface damage was analysed with a scanning electron microscope (SEM) to identify the wear mechanisms. Additionally, atomic force microscopy (AFM) was conducted in order to obtain roughness of the surface damage at 60°. The results indicated that higher amount of mass loss was obtained by angular silicon carbide particles.     

低温离子渗碳对304不锈钢耐磨性影响的研究

为了提高奥氏体不锈钢零件的使用寿命,扩大其使用范围,本文以304不锈钢为研究对象,通过试验方案的设计,采用了低温离子渗碳方法,在不同条件下进行试验,主要对其显微硬度和摩擦性能进行对比分析。结果表明,在一定条件下,低温离子渗碳后,由于奥氏体不锈钢中有过饱和的碳原子渗入,引起奥氏体晶格发生畸变,产生残余应力,使得304不锈钢表面硬度及耐磨性均明显改善,提高了其使用寿命,也说明了渗碳温度显著影响不锈钢的性能。     

Failure analysis of melt urea pump impeller

Abstract

A melt urea pump is out of work after only 6 days in service. The failure of the melt urea pump impeller is analysed using different methods including chemical composition analysis, metallographic observation, SEM and energy dispersive spectroscopy analyses, etc. The results show that the material of the impeller is not the reported AISI 321 stainless steel but AISI 316 stainless steel. There are many honeycombed holes on its impeller, which is the typical feature of cavitation damage. Therefore, the main failure reason of the impeller is the cavitation erosion, and the electrochemical corrosion of the medium also accelerated the failure of the impeller. The failure of the impeller is not related with the as casted defects of the material because no obvious as casted defects are found in the material.     

Design and performance of a high velocity air–sand jet impingement erosion facility

This paper describes the design, construction and capabilities of a high velocity air–sand erosion rig. It has been designed with the aid of computational fluid dynamics to approximately simulate the erosion conditions often experienced by subsea choke valves used in the offshore oil industry. It has also been designed to evaluate the erosion performance of CVD diamond coatings at sonic velocity. The rig is of the gas-blast design in which solid particles, typically sand 60–660 μm in size, are injected into a high velocity air stream and accelerated down a 16-mm-diameter tube, 1 m in length, before striking the sample under test. Tests can be carried out with particle velocities of up to 340 m/s under a wide range of sand fluxes, impact angles and standoff distances. The results of pressure, velocity and sand flux calibration work are described. In addition, preliminary experimental data on tests carried out on mild steel, bulk and sprayed tungsten carbide are also presented. The flexibility of the air–sand rig allows the erosion behaviour of materials to be studied under a wide range of conditions.