Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-31 Cooperative journals: 《中国腐蚀与防护学报》
Abstract： Corrosion is a very common and serious problem which has a harmful impact on the economy development of the country. Among others the application of organic paints is the most economical and efficient way to protect engineering structures from corrosion. Fluorocarbon paint is one of the most widely used resins for anticorrosion application due to its excellent corrosion resistance, chemical resistance，and weatherability. However, fluorocarbon paint also has some disadvantages restricting its application in some fields, so it is necessary to modify the fluorocarbon paint. In this article，the development history and application of the fluorocarbon paint were systematically summarized. Then various modification methods including chemical modification, physical blending, and filler modification used for enhancing the anti- corrosion performance of fluorocarbon paint were introduced. Finally, the development trend of fluorocarbon paint was forecasted.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-31 Cooperative journals: 《材料研究学报》
Abstract： Ingeneral,high- temperature salt- corrosion may usually induce mechanical stresses and phase transformation within ZrO2，as the main componentof thermal barrier coatings (TBCs), therewith further cause the failure of TBCsfor hot section components of gas turbine. Yb/Y co-doped zirconia (YbYSZ) powder was synthesized by a coprecipitation- calcination method, thenYbYSZ ceramic pallets were obtained by cold pressing and subsequent sintering at high temperature. The corrosion behavior of thepallets coated with a film of powder mixture CaO-MgO-Al2O3-SiO2 (CMAS) was examined in air at 1250℃ for different time intervals. The elemental diffusion and phase transformationwith YbYSZ after high-temperature corrosion wereinvestigated by XRD, SEM and EDS. The results showed that among othersthe elementYbin YbYSZ reacted preferenyially with CMAS and dissolved into the molten saltCMAS. The loss of Yb could suppressed the segragation of Y from the rest YbYSZ.Consequently, it stabilized the metastable tetragonal phase (t'-zirconia). The optimal dose of Yb is 5 mass% for the minimal yield of monoclinic ZrO2 in the YbYSZ after corrosion test.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-19 Cooperative journals: 《金属学报》
Abstract： Alloy 825 is widely used for chemical and petrochemical applications due to its good combination of mechanical properties and corrosion resistance. However, intergranular corrosion (IGC) is one of the serious problems for alloy 825 exposed to aggressive environments, which could result in unexpected failures and lead to huge losses. The grain boundary structure, which can partly be described by coincidence site lattice (CSL) model, can influence the grain boundary chemistry and the susceptibility to intergranular corrosion. The field of grain boundary engineering (GBE) has developed a lot over the last two decades since the concept of grain boundary design was proposed. The aim of GBE is to enhance the grain-boundary-related properties of materials by increasing the frequency of low ΣCSL (Σ≤29) grain boundaries (GBs) and tailoring the grain boundary network. It was reported that in some fcc materials with low stacking fault energy, such as Ni-based alloys, lead alloys, austenitic stainless steels and copper alloys, the frequency of low ΣCSL GBs can be greatly increased by using proper thermomechanical processing (TMP), and as a result the grain boundary related properties were greatly enhanced. In this work, GBE is applied to the manufacture of Ni-based alloy 825 tubes by cold drawing using a draw-bench on a factory production line and the subsequent annealing. The effect of thermomechanical processing on the grain boundary character distribution (GBCD) of alloy 825 was studied by means of the EBSD technique and orientation image microcopy (OIM). The results show that the proportion of low ΣCSL grain boundaries increase to more than 75% by the TMP after 5% cold drawing and subsequent annealing at 1050 ℃ for 10 min, and simultaneously the large- size highly-twinned grain- cluster microstructure is formed. The size of the grain- cluster and proportion of low ΣCSL grain boundaries decrease with the increase of pre-strain. The proportion of low ΣCSL grain boundaries decreases with the increase of the mean grain size. The annealing temperatures in the range of 1050~1125 ℃ have no obvious effect on the GBCD of the specimen with 5% cold drawing deformation; while the proportions of low ΣCSL GBs of the sample with 3%, 7% and 10% cold drawing deformation decrease with the increase of annealing temperature.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-19 Cooperative journals: 《金属学报》
Abstract： Deep cryogenic treatment (DCT) is a supplement to conventional heat treatment, which usually involves cooling the material to liquid nitrogen temperature around -196 ℃ for a given soaking time and then heating back to the room temperature. As claimed in many pioneering researchers, DCT can evidently improve the hardness and wear resistance of high-carbon high-alloy steel and has been widely used to die steels, cutting tools, carburizing steels and barrels. The improvement of mechanical properties by DCT can be attributed to the transformation from retained austenite to martensite, the fine dispersion of nanoscale carbide precipitate and the removal of residual stresses. However, the nanoscale carbide precipitate is still lack of evidence and the interpretation of carbon segregation behavior during DCT is still unconvincing. In this work, the high-carbon high-alloy steel SDC99 is first austenized at 1030 ℃ for 30 min and then immersed in liquid nitrogen for 8 h and finally tempered at 210 ℃ for 2 h. The spatial distributions of carbon atom and alloy element concentration in quenched, DCT treated and tempered samples are analyzed by three dimensional atom probe (3DAP), respectively. In addition, the axial ratio and carbon content of martensite are studied using XRD and the carbide morphology before and after DCT are also observed in situ by SEM. The results indicate that after quenching from 1030 ℃ to room temperature, the volume fraction of retained austenite in SDC99 is about 21.1%. The retained austenite is soft and unstable which can easily transfer to martensite at lower temperatures. Carbon atoms will segregate slightly due to self-tempering. However, other alloy atoms do not segregated with carbon atoms. After quenching from 1030 ℃ to room temperature and then cooling in nitrogen for 8 h, the volume fraction of retained austenite in SDC99 will decrease to 7.4%. Carbon atoms will segregate along the twin boundary of martensite and form a segregation area with a thickness about 5~10 nm.There is no carbide precipitate after DCT. Furthermore, carbon atoms segregate again during heating up back to room temperature from -196 ℃. After tempering at 210 ℃ for 2 h, the volume fraction of retained austenite is almost 5.4%. Both carbon and alloy atoms will segregate during tempering at 210 ℃. With the increase of tempering time, the carbon segregation will aggravate and result in a C-rich phase or form the M23C6 carbide combined with other alloy element. This is one of the main reasons increasing the wear resistance of tool steels.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-18 Cooperative journals: 《材料研究学报》
Abstract： Mg doped hydroxyapatite coatings with 0, 0.28%, 0.32%, 0.49% Mg respectively, as artificial human bones were prepared on carbon / carbon composites by means of electromagnetic induction method. Then they were characterized by SEM, EDS, X- ray diffraction and Fourier transform- infrared spectroscopy etc. The results show that Mg ions entered the hydroxyapatite lattice and these coatings have only a little difference in constituents. Within the range Mg content of human bone, Mg ions can enhance the adhesion, multiplication, and differentiation of external osteoblasts.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-18 Cooperative journals: 《材料研究学报》
Abstract： High temperature oxidation performance of ZG40Cr25Ni20 steel and a kind of low nickel austenitic heat resistant cast steel were comparatively investigated by means of isothermal oxidation test, scanning electron microscope(SEM) with energy dispersive spectrometry (EDS) and X- ray diffraction analysis. The results show that a protective oxide scale Cr2O3 forms at the interface of substrate and the outer oxide scale, which can certainly block the inward diffusion of oxygen ions and the outwards diffusion of metal action, thereby reducing the oxidation rate, therefore, the heat-resistant cast steel exhibits better high temperature oxidation resistance in comparison with the ZG40Cr25Ni20 steel, whilst the nickel saving steel contains lower Ni but a little higher Cr and Mn than the ZG40Cr25Ni20 steel.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-18 Cooperative journals: 《材料研究学报》
Abstract： Effect of linear heating aging process and the Cu content on the performance and the formation of precipitates of Al-Zn-Mg-(Cu) alloy was investigated by means of differential scanning calorimeter (DSC), hardness tester, transmission electron microscopy(TEM) and three- dimensional atom probe (3DAP). The results show that with the increase of the aging temperature the hardness rises firstly and then decreases after reaching a peak. After aging at every selected temperature of the linear heating aging treatment process, all the relevant hardness of the Al-Zn-Mg-Cu alloy is higher than that of the Al-Zn-Mg alloy. After aging at peak point by linear heating, the main precipitates are η' phase, while there exists small quantities of η phase and GP zone for the two alloys Al-Zn-Mg and Al-Zn-Mg-Cu. However the addition of Cu may induces certain change of the composition and morphology of the precipitates and delay their transition from metastable state to stable state.
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