| Titanium alloys are widely used in many fields of modern production and life because of their special properties.Titanium alloys will produce relatively serious oxidation during hot processing.The oxide not only causes waste of materials,but also seriously affects the mechanical properties of the alloy and the surface plasticity and toughness,and it brings great difficulties to the hot processing of titanium alloys.Therefore,it is very important to solve the oxidation problem of titanium alloy during hot processing.In this paper,based on the high-temperature oxidation protection mechanism and design principles of glass coatings,a composition of coated glass powder was designed.A high temperature oxidation resistant glass coating was prepared on the surface of TC4 titanium alloy by high temperature solid phase reaction method,and the high temperature oxidation resistance of the glass coating was characterized.The main research works are as follow:（1）According to the inert melt film shielding protection mechanism of glass coating,the design principles of glass coating are high temperature resistance,good stability,good wettability,and environmental friendliness.By comparing the free energy and stability of Ti O2to those of the other various oxides,a formula was designed as 44.0wt.%Si O2、25.0wt.%B2O3、1.7wt.%Al2O3、10.0wt.%Na2O、7.5wt.%Ca O、6.8wt.%Mg O and 5.0wt.%Ti O2glass powder.（2）The borosilicate glass powder was prepared by the high-temperature solid-phase reaction method.The DSC test verified that the softening temperature of the glass powder was low（about 600°C）,and it was suitable for preparing glass coatings for titanium alloy thermal processing.According to the glass powder:2%methylcellulose M450 aqueous solution binder:distilled water solvent=2:1:2 mass ratio,the gray suspended glass powder slurry was prepared with appropriate viscosity,environmental friendliness and good dispersibility.Then a layer of glass coating with a thickness of about 0.15～0.3mm was prepared on the surface of TC4 titanium alloy by dip coating.（3）Through the oxidation weight gain experiment,the oxidation weight gain,thickness of the oxide layer,and the hardness from the surface layer to the core were used to characterize the oxidation protection performance of the glass coating.After holding the TC4 titanium alloy samples at 650℃,750℃,850℃,950℃and 1050℃for 2h,the oxidation weight gain of the coated titanium alloy sample decreased by94%,93%,79%,75%and 85%,respectively compared with that of the uncoated samples,and the oxide layer thickness of the glass coating sample was reduced by30μm,55μm,75μm,250μm and 270μm,respectively,compared with the uncoated samples.The maximum hardness of the surface of the coated titanium alloy was about HV400 lower than that of the uncoated titanium alloy at 650℃～950℃,and HV800lower at 1050℃.（4）The surface morphology of the glass coating was observed with a scanning electron microscope,and it was found that the glass coating gradually softened and melted into a film with the increase of temperature.Through XRD phase detection,it was found that the glass coating was amorphous before 750°C,and Ca Mg Si2O6mainly appeared at 850℃～1050℃and a small amount of Ca B2O4or Na（Al Si3O8）crystal phases.The higher the temperature,the less the crystal phase was;The TC4titanium alloy oxide was mainly Ti O2crystal phase.The above studies have shown that the borosilicate glass coating developed in this subject has a satisfactory anti-oxidation protection effect on titanium alloys at the processing temperature of TC4 titanium alloys. |
