Structural And Mechanical Prediction Of Titanium Foams

The prediction problem of porosity and mechanical property is a big challenge for all kinds of preparation methods of titanium foams, especially at this current the research of titanium foam still stay in the laboratory, which makes this problem become particularly important.Although there has been a attention to this problem at home and abroad, especially in developed countries such as the US, Europe and Japan, the research is still in the preliminary stage at present. This paper has carried on a beneficial attempt. On the basis of literature reviews, the porosity and mechanical properties of titanium foams prepared by varied parameters of space holder were studied. The reproducibility of porosity and mechanical properties was also studied. The relationship between porosity and spacer content were deeply analyzed. Some valuable results were obtained and the major contribution of present paper were shown as the followings:(1)A review was given to the progress in fabrication of titanium foam. The novel fabrication methods of titanium foam were comprehensively summarized since 2004. And, a classification was introduced.The development tendency of fabrication methods of titanium foam was proposed by comparing the technical feature of these methods.(2)A review was given to the research status and developments of titanium foam prepared by the method of space holder technique. The development direction of titanium foam prepared by space holder techniquewas proposedby introducing the features of these space holders.(3)According to the difficulty of preparation of titanium foam, an ideal that the removal parameters of space holder were based on its thermal analysis results was proposed. The thermal analyzer was used to measure the serves of thermogravimetry and differential scanning calorimetry of carbamide. The removal atmosphere, heating rate and final temperature of space holder were selected based on these curves. As a result, the problem of collapse during fabrication of titanium foams with high porosity was resolved. The problem of oxidation in the surface of titanium powder can be effectively avoided by separating the removal of space holder and the sintering of titanium powder during high temperature into two steps. In the case of the spacer contents excess 60%, titanium foams with porosities in the range of 50.2-71.4% was obtained. The results show that the porosity was lower than the spacer content.(4)A theoretical analysis was given to the influence of spacer size on porosity. Three different sizes of space holder particle was obtained by sieved. The case of the same spacer content, the results show that on the one hand the porosities were all lower than the spacer content, on the other hand the porosity slightly decreases as decreasing the size of space holder. The analysis results indicate that the decreased volume of macropores slightly increases as decreasing the size of space holder by assuming the macropores shrink their volume during sintering.(5)The concept of reproducibility of porosity and mechanical properties was proposed. The results show that the porosity was reproducible while the reproducibility of mechanical properties was poor, which can be improved by increasing the content or decreasing the size of space holder. It was found that the poor reproducibility of mechanical properties was mostly attributed to the factors as uncontrollable distribution of macropores through a discussion.(6)Thevolume change of macropores obtained by the removal of space holder during sintering was argued. It proves that the macropores shrink their volume during sintering based on theory and practice. When the reduced volume of macropores larger than the volume of micropores in the cell-walls, it will cause the porosity less than the spacer content.(7)Amathematical model between porosity and spacer content was established. It proves that the relationship between porosity and spacer content is linear, which realizes the prediction of porosity based on theory and practice. Combined with the model equation of Gibson-Ashby, it realizes the prediction of mechanical properties via spacer content.