Yin Zhongda

Study of double layer rare earth metal conversion coating on aluminum alloy LY12

The process of the double layer rare earth metal (REM) conversion coating on aluminum alloy LY12 (2024) was introduced in this paper. The corrosion resistance of REM conversion coating was examined by electrochemical impedance spectroscopy. The results showed that the coating increased the corrosion resistance (Rp) of the alloy surface, thus reducing the driving force of corrosion. The morphologies of the coating were studied by scanning electron microscope. The results revealed that the coating consisted of layers of spherical particles with different size, which grew gradually to cover the surface of aluminum alloy. The X-ray diffraction analysis revealed that the film was amorphous. The results of X-ray photoelectron spectroscopy indicated that the film consisted of cerium(III and IV) oxide and cerium(III and IV) hydroxide.

Hydroxyapatite-Ti functionally graded biomaterial fabricated by powder metallurgy

Abstract A functionally-graded biomaterial (FGM) in a hydroxyapatite (HA)–Ti system was developed by an optimized powder metallurgical process and investigated by microstructural analysis and mechanical tests. The constituents in sintered HA–Ti FGM distribute gradually with the variation in chemical composition, eliminating the macroscopic interfaces, such as that in HA–Ti direct joint. Partial decomposition of HA phase was found in interlayers of the FGM due to the co-existence of Ti during sintering. Mechanical properties in HA–Ti FGM also exhibit gradient distributions. Vickers hardness and Young’s modulus are strongly affected by the porosity. However, bending strength and fracture toughness increase remarkably with the rise of Ti content, especially in the Ti-rich region. Maximum strength and toughness (971.96 Mpa and 29.691 MPam 1/2 respectively) were reached in the pure Ti layer, which are far higher than those of human bone. In addition, the strengthening and toughening mechanism was discussed. In summary, HA–Ti FGM is a promising biomaterial for use as a hard-tissue replacement implant, considering its mechanical behaviors.

Corrosion behavior of rare earth metal (REM) conversion coatings on aluminum alloy LY12

The processes of the double layer rare earth metal (REM) conversion coating on aluminum alloy LY12 (2024) were introduced. The results of polarization tests showed that the corrosion resistance of the double layer REM conversion coating was superior to that of chromate conversion coating. The corrosion behavior of REM conversion coatings on LY12 alloy was studied with optical microscopy and energy dispersive spectroscopy (EDS). The results showed that in NaCl solution, pits initiated on the coatings formed on Cu-rich intermetalics. According to the equivalent circuit of pitting, a new method for analyzing the pit growth of REM conversion coatings was put forward by employing electrochemical impedance spectroscopy (EIS). Transmission line W in equivalent circuit could be neglected in short term exposure of REM conversion coatings to NaCl solution. This led to a formula for calculating the area fraction of pitting (F) on the surface of REM conversion coatings by simplifying the equivalent circuit

Fabrication and microstructure of ZrO2/NiCrCoAlY graded coating by plasma spraying

Abstract An 8 wt% Y2O3-ZrO2/NiCrCoAlY graded coating was fabricated on a TC4 (Ti-6Al-4V) surface by air plasma spraying. Microscopic analysis showed that the ZrO2/NiCrCoAlY graded coating exhibits a stepwise distribution in composition from metallic bond layer to ceramic top layer, consisting of t′-ZrO2 phase and supersaturated Ni-based solid solution phase, and displays tight coherence with the TC4 substrate. In addition to mechanical combination, chemicometallurgical reaction combination occurs at some locations and small amounts of NiTi2 and TiAl3 phases at the coating-substrate interface develop during spraying.

Fuzzy modeling of predictionM s temperature for martensitic stainless steel

A method of fuzzy modeling based on fuzzy clustering and Kalman filtering was proposed for predicting Ms temperature from chemical composition for martensitic stainless steel. The membership degree of each sample was calculated by the fizzy clustering algorithm. Kalman filtering was used to identify the consequent parameters. Only Grade 95 steel are available for training and validation, and the fuzzy model is valid for the following element concentration ranges (wt%): 0.01<C<0.7; 0<Si<1.0; 0.10<Mn<1.25; 11.5<Cr<17.5; 0<Ni<2.5; 0<Mo<1.0. Compared with that of several empirical models reported, the accuracy of the fuzzy model was almost 5 times higher than that of the best empirical model. Furthermore, the compositional dependences of Ms were successfully determined and compared with those of the empirical formulae. It was found that the specific element dependences were a function of the overall composition, something could not easily be found using conventional statistics.