| The vent valve is a key part of the internal-combustion engine, whose working temperature is 600-800℃generally and reach to the most above 850℃. As a result of the air valve operating with high-speed under the high-temperature environment, the head possibly produces the heat fatigue except that it possibly appears the machinery fatigue. With the heat energy engine development to the high temperature, the high stress and the high effective direction, the vent valve will be undergo a more serious function with the high temperature, the high stress, the thermal shock, the fuel gas corrosion and the granule undermining. So it is a higher request to the engine material performance.In this experiment the solid powder method with no industry pollution was adopted to the 4Cr10Si2Mo and 4Cr14Ni14W2Mo air valve steel to infiltrate multi-element. To add Cr, Al, Ti and so on as the main components in the coatings is to resist the high temperature corrosion, at the same time to add a lanthanum element is to may activate and purify a work piece surface and urge to infiltrat. The microstructures of the infiltrating coating had been observed by the light microscope, And the phase making-up of the infiltrating coating microstructures and the element diffractions had been determined by using the XRD and the electron probe. The hardness values of the infiltrating coatings from outward to inner had been determinated through the hardness measuring instrument. In order to inspect the toughness and the anti-flaking ability of the infiltrating coatings of the different matrices in a fast cycle temperature field we had done the thermal fatigues experiment under the circulation condition heated to 650℃and cooled to 20℃.Finally the thick crystal particle formed in the matrices material while solid permeating was made subdivided through normalizing and quenching two kinds of crafts. The result shows, all the specimens after Al-Cr,Al-Cr-Ce,Al-Ti,Al-Ti-Ce infiltrating under 1100℃have a superier anti-high temperature oxidability and a higher hardness degree;Adding the lanthanum element Ce the infiltrating speed can be obviously improved , and the coating is thicker and the average hardness degree of the coatings is higher in the same condition. The results of the thermal fatigue examination indicate that the crackle is apt to germinate and expand at rich-Al zone when the aluminum element gathers in the coatings;When the aluminum distributes in the coatings as dispersing components, there is the fine thermal fatigue performance. A crackle generally will be not appear between the different matrices and the coatings, and they combine very well. Al-Cr-Ce infiltrating coatings of M body has the fine thermal fatigue performance and it appears the micro-crackle under the thermal cycle above 40 times. The normalizing and quenching crafts have the obvious function on the thick crystal particle in the matrices,and the crystal degree of M body has been subdivided from 6-7 grade to 2-3 grade. |
