Titanium alloy is widely used in military and civil fields because of its high strength, corrosion resistance and high specific strength. However, high temperature oxidation reaction will occur when it is used in a high temperature environment, which reduces its performance and limits its application range.Ceramic coatings are prepared in situ on the surface of titanium alloy by means of Micro⁃arc oxidation(MAO) technique. The combining capability of ceramic layer and metal substrate is very strong, has good wear resistance, corrosion resistance and resistance to high temperature and other characteristics, the technological process is simple and efficient, low cost and is friendly to the environment, can greatly improves the oxidation resistance of titanium alloy, prolong its service at high temperatures.This paper reviews the research status of micro⁃arc oxidation technology in the field of high temperature oxidation resistance of titanium alloys.The influences of reaction parameters, electrolyte, reaction time and power mode on the structure and high temperature oxidation resistance of micro⁃arc oxide ceramic coatings are summarized.

In order to solve the problem that the angle of crack and magnetization direction was too small to identify in the pipeline magnetic flux leakage internal detection, the influence of crack angle on magnetic flux leakage detection signal and the characteristics of crack magnetic flux leakage signal under the condition of axial excitation of DC electromagnet were analyzed. Comsol finite element simulation software was used to simulate and analyze the crack defects of 0.2 mm in different angles of the inner wall of the pipeline. DC electromagnet axial excitation experimental platform was built, and EDM technology was used to process the specimens with different angles of crack to carry out the dragging experiment of the crack angle. Results show that the minimum detectable angle of crack and magnetization direction is 25°. The peak value of MFL signal decreases with the decrease of crack angle, larger the signal span, the greater the influence of noise signal. When the magnetization direction is perpendicular to the crack, the maximum span of MFL signal amplitude is the smallest, and when the magnetization direction is parallel to the crack, no MFL signal is generated.