工程科学学报 (Jun 2018)
Viscosity-temperature characteristics, hot corrosion, and thermal barrier properties of new glass lubricants containing NaCl for the extrusion of titanium alloys
Abstract
To improve lubrication during the hot extrusion of titanium alloys, a new type of glass lubricant based on phosphate glass, SiO2, and NaCl was prepared. The viscosity-temperature curve of the lubricant with different composition ratios was determined from an extrusion experiment. Corrosion by the lubricant of a titanium alloy under high temperature was analyzed via scanning electron microscope. The heat transfer characteristics between the titanium alloy and die steel was studied using heat transfer coefficient measurement equipment. The results show that the viscosity of the glass lubricant, with a mass ratio of phosphate, SiO2, and NaCl of 70:20:10, varies slightly between 600℃ and 900℃, ranging from 1.3×105 to 9.4×105 Pa·s. This is beneficial to improvements in the extrusion and lubrication of titanium alloys. When the contact time between the new glass lubricant and the titanium alloy is not more than 3 min at 950℃, the new glass lubricant shows little corrosion on the surface of the titanium alloy, and serves the function of removing the original oxide layer on the alloy surface. High-temperature corrosion of the titanium alloy surface increases gradually with an increase in contact time. When the initial temperatures of the TA15 titanium alloy and H13 die steel are 900 and 400℃ respectively and the final thickness of the new glass lubricant is approximately 0.1 mm, the heat transfer coefficient between the titanium alloy and die steel increases from 185 to 1714 W·m-2·s-1 with an increase in contact time. In a traditional silicate glass lubricant, used in the hot extrusion of titanium alloys, the heat transfer coefficient increases from 286 to 2025 W·m-2·s-1. This demonstrates that the proposed glass lubricant exhibits better thermal barrier properties at high temperatures than the traditional one.
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