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。     

Cavitation erosion of aluminium alloys

Cast aluminium-silicon, cast aluminium-zinc and mechanically alloyed aluminium alloys were eroded in distilled water using a 20 kHz ultrasonic vibratory device. The erosion was measured by weight loss, and the damaged surface was examined using metallographic and profilometric techniques. The maximum differences in the incubation period, in the linear erosion rate and in the mass loss after a 10 h exposure for the nine materials investigated were 620%, 740% and 250%, respectively. The mechanically alloyed materials had by far the best combination of erosion properties. The cast Al-Si alloys had the poorest resistance to erosion. Age hardening was particularly beneficial with the Al-Si alloy. The main mechanism of material removal in all the alloys is by plastic deformation and ductile fracture.     

Cavitation erosion resistance of heat-treated NiTi

NiTi (Ti–50.8 at.% Ni) specimens were solution-treated at 1000 °C, followed by aging between 200 and 600 °C. The cavitation erosion resistance of all the aged specimens in deionized water was improved relative to the solution-treated specimen, with a maximum increase of about 8.7 times, which was achieved by aging at 500 °C. The results also indicate that both austenite and martensite contribute to the high cavitation erosion resistance of NiTi. It is also shown that a simple macro-indentation test employing a Rockwell indenter may be used for preliminary screening of heat-treated NiTi with respect to cavitation erosion resistance.     

Cavitation damage to geomaterials in a flowing system

Short-time cavitation erosion of rocks and cementitious composites is investigated in a laboratory flow cavitation chamber. Cavitation erosion with an exposure time as low as 10 seconds generates measurable damage. Mineral composition plays a major role in the cavitation erosion of the material. The erosion mainly occurs in an intergranular or intercrystalline mode, respectively. Fracture toughness of rock and conventional concrete is a good indication of cavitation erosion resistance. However, density is a second important evaluation parameter; materials with a low degree of pre-existing flaws, namely glass and high-strength silica cement, show an extraordinary high erosion resistance. The cavitation erosion of the rock materials tested in this study is always higher than that of conventional concrete mixtures. Elastic strain energy density is not a measure of cavitation erosion resistance of rocks and cementitious composites. A parameter = d _M · E _M · _M/K _Ic ⁿ is derived to approximate the cavitation erosion resistance of the materials. The parameter n is a function of the R-curve-behavior.     

Cavitation erosion behavior of laser-clad Ni-Cr-Fe-WC on brass

Laser surface modification of brass with an alloy-ceramic composite powder Ni-Cr-Fe-WC was studied using a two-step process, with powder preplacement followed by laser irradiation. For preplaced coatings of a few 100 μm thick, successfully cladding/alloying was achieved at a laser (CW Nd:YAG) energy density in the range 60-100 J/mm². Under proper processing conditions, the cavitation erosion resistance was increased by a factor of 9.1. This large increase was attributed to the formation of a Ni-rich matrix reinforced by precipitated carbides and tightly bound WC particles.     

Cr-Ni-Mo双相不锈钢的空泡腐蚀行为

利用超声波空蚀实验装置对Cr-Ni-Mo奥氏体-铁素体不锈钢及其同质材料堆焊后的堆层金属在自来水溶液中的空蚀行为进行了研究.通过扫描电镜（SEM）、显微硬度计等检测设备研究了材料空蚀表面形貌和微观结构.结果表明：Cr-Ni-Mo双相不锈钢的抗空蚀性能明显优于经TIG（钨极惰性气体保护焊）表面堆焊后的堆层金属试样;双相不...     

Cavitation erosion behavior of nitinol coating sealed by epoxy resin

The nitinol coating against cavitation erosion was prepared by air plasma spraying and sealed with epoxy resin successfully. After the coating sealed with epoxy resin, the pores and cracks of the coating were filled with the epoxy resin and then the cohesiveness between the lamellae was improved, the hardness increased from 3.68 GPa to 7.49 GPa, the energy recovery ratio (superelasticity) was improved from 41.9 % to 49.0 % and the toughness was enhanced from 0.011 GPa to 0.045 GPa. During the cavitation erosion test, the epoxy resin reduced the cavitation resources and absorbed the impact energy from the micro-jet or shock waves. Meanwhile, the high hardness and superelasticity can help the coating to resist cavitation erosion and the high toughness can delay the expansion of cracks during the cavitation erosion test. As a result, after cavitation erosion for 300 min the cumulative mass loss of the coating sealed by epoxy resin was 1/5 times as much as that of the nitinol coating without sealing. Therefore, the cavitation erosion resistance of the nitinol coating can be improved by sealed with epoxy resin.     

Fe-25Mn-6Si-7Cr形状记忆合金空蚀研究

用旋转圆盘实验机研究了Fe—25Mn—6Si—7Cr形状记忆合金空蚀．结果表明，Fe—25Mn—6Si—7Cr形状记忆合金空蚀是一种疲劳破坏，失效机制为沿晶断裂和晶内蚀坑．Fe—25Mn—6Si—7Cr形状记忆合金空蚀的速度效应小，抗空蚀性能在34m／s和45m／s速度下分别是对比材料0Crl3Ni5Mo不锈钢的1．6倍和7．3倍．伪弹性是F1—25Mn—6Si—7Cr形状记忆合金具有高抗空蚀性能的主要原因．     

Rain erosion damage in brittle materials

In order to understand the processes involved in the high-velocity rain erosion of brittle materials the impact damage produced in soda-lime-silica glass by single and multiple jet impact was studied. The damage was quantified by measuring the post-impact strength of specimens. It is shown that the impact damage depends on the impact velocity, the number of impacts and the specimen dimensions. A new analysis for calculating the velocity dependence of jet/drop impact damage in brittle materials is presented. The model is based on Hertzian contact analysis and dynamic fracture mechanics and takes into account the statistical nature of the flaws in the specimen. A good qualitative agreement with experimental results is obtained.     

Cavitation erosion resistance of 13/4 and 21-4-N steels

Nitrogen strengthened austenitic stainless steel (termed as 21-4-N steel) in as cast and hot rolled conditions has been investigated as an alternative to 13/4 steel (termed as CA6NM) to overcome the problems of cavitation erosion in hydro turbine underwater parts. The cavitation erosion of 21-4-N and 13/4 steels was investigated by means of an ultrasonic vibration processor. The cavitation erosion is highly dependent on microstructure and mechanical properties. The results show that hot rolled 21-4-N steel is more cavitation erosion resistant than the 13/4 and 21-4-N steels in as cast condition. The eroded surfaces were analysed through optical microscope and scanning electron microscope for study of erosion mechanisms.     

Material-point erosion simulation of dynamic fragmentation of metals

We present a validation assessment of the eigenerosion scheme applied in conjunction with the Optimal Transportation Meshfree (OTM) method. The assessment is based on the detonation-driven 304L steel spherical-cap fragmentation experiments of Campbell et al. (2007). Metrics used for purposes of validation include the velocity history of a witness point of the shell and the histogram of recovered fragment sizes. The results of the simulations are found to be in overall good agreement with the experimental measurements, especially when allowances are made for uncertainties in the characterization of the drive and material properties. The ability of the approach to predictively simulate exceedingly complex patterns of fracture and fragmentation under severe conditions of loading and material behavior is remarkable, especially in consideration of the simplicity of the fracture model and its implementation.     

Cavitation erosion resistance of Fe-26Mn-6Si-7Cr-1Cu shape memory alloy

Abstract

The cavitation erosion of low stacking fault energy Fe-26Mn-6Si-7Cr-1Cu shape memory alloy has been investigated in water using an ultrasonic vibratory apparatus, and compared with the behaviour of 0Cr13Ni5Mo stainless steel. It is shown that Fe-26Mn-6Si-7Cr-1Cu alloy has higher cavitation erosion resistance than 0Cr13Ni5Mo stainless steel. The cavitation erosion mechanism of Fe-26Mn-6Si-7Cr-1Cu was studied by examining the eroded surface using X-ray diffraction (XRD) and scanning electron microscopy (SEM). During early stages of cavitation erosion, Fe-26Mn-6Si-7Cr-1Cu alloy undergoes strain induced martensitic transformation. Exposure to further cavitation results in the deformation of ? martensite. The boundaries of ? martensite impede plastic deformation, leading to strain accumulation and subsequent material removal. On the basis of an XRD study and indentation tests, the better cavitaton erosion resistance of Fe-26Mn-6Si-7Cr-1Cu alloy is mainly ascribed to strain induced martensitic transformation, which can absorb impact energy without damage.