Materials Science Forum Vol. 950

Abstract: Cavitation erosion (CE) behavior of 2205 duplex stainless steel (DSS) under high pressure was investigated by using water jet apparatus, which designed according to ASTM G134-95. The effects of the nozzle diameter and target distance on mass loss were analyzed. The CE behavior of 2205 DSS was evaluated by cumulative mass loss with time, and the incubation period and the CE rate were calculated by fitting results. From the scanning electron microscope (SEM) observation, it is found that the surface of 2205 DSS was damaged slightly during the CE incubation period and eroded dramatically in the accelaration stage. The energy dispersive spectrometer (EDS) results showed that the Ni content in the erosion area appeared obviously lower in comparison with the non-erosion area. Meanwhile, the content of Ni in ferrite was also detected to be clearly lower than in austenite with electron back scattered diffraction (EBSD) and EDS mapping techniques. Therefore, it could be concluded that CE take place selectively on the 2205 DSS surface, the damages were initiated and progressed in ferrite phase prior to in austenite phase.

Abstract: This paper provides a comprehensive review of developments and progress made in martensitic heat-resistant steels, especially, with the emphasis on strengthening mechanisms used in elevated temperatures. We desired to elucidate the correlation between high creep resistance at elevated temperatures and thermal stability of nano-sized particles precipitated from martensite matrix. Finally, future prospective strengthening methods for martensitic heat-resistant steels were discussed.

Abstract: This paper proposes a two-step homogenization heat treatment to dissolve the eutectic structure and long period stacking ordered phase (LPSO) formed during solidification into the α-Mg matrix. The microstructure evolution and mechanical properties of Mg–7Gd–3Y–1Nd–2Zn–0.5Zr alloy during the two-step homogenization heat treatment have been investigated systemically. The results reveal that as-cast alloy is composed mainly of α-Mg, (Mg,Zn)₃RE, eutectic phase, stacking fault, block-like LPSO phase and square-shaped compounds rich in RE. The HRTEM results suggest that the block-like long period stacking ordered phase in as-cast alloy is 14H-type rather than 18R structure, and the stacking sequences of the 14H-LPSO phase are ABABACBCBCBCAB. After the first step homogenization of 520°C for 48 h, the eutectic structure has dissolved into the matrix, whereas the 14H-LPSO phase remains in the alloy. To further dissolve the LPSO phase into matrix, the second step homogenization of 540°C for 24h was adopted. After the second-step of homogenization, the residual 14H-LPSO phase has dissolved into the matrix totally. The as-homogenized alloy is composed mainly of α-Mg and square-shaped compounds rich in RE. The tensile tests at room temperature (RT) exhibit that the ultimate tensile strength (UTS), yield strength (YS) and elongation of as-cast alloy are 172 MPa, 128MPa and 2.8%, whereas the UTS, YS and elongation of as-homogenized alloy are 253 MPa, 185 MPa and 8.4, respectively.

Abstract: This paper aims to analysis the effect of coolant parameters on surface roughness in internal cylindrical grinding of annealed 9CrSi steel. The concentration and flow rate of the coolant are investigated in thirteen experiments by central composite design and response surface method. The effect of each parameter and their interaction on the surface roughness are analyzed by their regression model. From that model, optimal parameters are determined to obtain the minimum surface roughness. The measured roughness matches with the predicted roughness from the regression model. This proposed is proven and it can be further applied for optimizing other machining processes.

Abstract: Through the experiment of cutting 1060 Aluminum Alloy by Abrasive Water Jet (AWJ), the surface roughness of material which is cut by AWJ is controlled by the cutting work pressure, cutting stand-off distance, cutting traverse speed and the abrasive diameter which used in AWJ. Measuring the cutting surface roughness of 1060 Aluminum Alloy by stereomicroscope and surfagauge, among the factor which can affect the surface roughness, the cutting traverse speed play a dominant role to control the surface roughness in the process of cutting. As the result of the surface roughness of 1060 Aluminum Alloy at different cutting depth is different, which can be separated in two different zones (Smooth area and Rough zone). As the result of experiment, the abrasive diameter has little effect to change the surface roughness between two different zones. The surface quality of rough zone can be improved when change the diameter of abrasive: with the diameter of abrasive increase, the surface quality of rough zone become better. A higher cutting pressure can improve the surface quality of the cutting surface of 1060 Aluminum Alloy. While increase the cutting traverse speed in the process of cutting can decrease the surface quality of 1060 Aluminum Alloy cutting surface. In a certain range, increase the cutting stand-off distance of AWJ can decrease the surface roughness of the cutting surface, and the roughness of cutting surface will change little when the stand-off distance increases to a certain extent.

Abstract: In the process of abrasive water jet (AWJ) cutting, there will produce a series of striation shape on the cutting surface of target. In this paper, we define such striation as cutting striation shape. The most research of this paper is the force situation and movement trajectory of water jet in the process of cutting. It is deduced by theory that the cutting surface striation shape is circular arc and find that the radius of circular arc is related to cutting velocity, cutting pressure and the property of cutting material. In the experiment, stainless steel 304 and aluminum 6061 were cut by AWJ and the result shows that the shape of the surface striation is arc-shaped in both material surface. At different cutting pressure, for a same material, K_R is a constant value which is only related to the property of cutting material.

Abstract: The laser engineered net shaping (LENS) system was used for the laser based manufacturing of a test geometry used to assess the performance of additive manufacturing systems. This system was preferred over a selective laser melting (SLM) system due to certain inherent benefits that would promote the manufacture of the test geometry where the SLM system had failed due to part delamination. The test geometry was successfully manufactured on the LENS system and machined to produce test specimen for mechanical testing and microstructural evaluation. Investigations revealed that the α-β lamellar microstructure was formed via in situ martensitic decomposition of the α’ structure. This resulted in promising yield and tensile strengths in excess of 900 MPa and high tensile elongation up to 13%.

Abstract: TRIP effect containing steel was well reputed by its high mechanical properties among the 1^st generation of Advanced High Strength Steel. High Silicon content was well established as an inhibitor for cementite precipitation at para-equilibrium condition. However, the effect of manganese as a powerful stabilizer for retained austenite was not much studied in TRIP-Steel. Thereby, the effect of high manganese content on the TRIP containing steel is studied in this research. As been observed from OM, and XRD results, it was found that as long as increasing Manganese content, the fraction of retained austenite increases. No doubt that enrichment of retained austenite throughout the matrix, beers a great impact on the plastic deformation character of the investigated steels, which was proved by using a uniaxial tensile test and determining the strain hardening exponent.

Abstract: Two-phase materials, such as α+β Titanium (Ti) alloys, are technologically important. A number of factors can affect deformation behavior, including the interaction stresses between phases, the crystallographic relationships between phases, and the morphology. As a result, the deformation mechanisms of two-phase alloys may be different from the individual single-phase materials. For example, twinning may not occur in a single phase material if the grain size is very small but twinning can occur in a very fine grained alloy if the second phase contributes to the interfacial stresses due to elastic interactions. Interaction stresses can result from the difference in the elastic properties of the two phases. In particular, these elastic interaction stresses can be quantified by the finite element method (FEM). In this paper recent developments regarding two-phase deformation mechanisms will be reviewed and the ramifications on mechanical behavior in regard to two-phase Ti alloys in particular and on two-phase metallic materials in general will be outlined.