Watanabe I, Watkins J H, Nakajima H, Atsuta M, Okabe T
Department of Biomaterials Science, Baylor College of Dentistry-Texas A&M University System, Dallas 75246, USA.
J Dent Res. 1997 Mar;76(3):773-9. doi: 10.1177/00220345970760031001.
In casting titanium using a two-compartment casting machine, Herø et al. (1993) reported that the pressure difference between the melting chamber and the mold chamber affected the soundness of the castings. This study tested the hypothesis that differences in pressure produce castings with various amounts of porosity and different mechanical properties values. Plastic dumbbell-shaped patterns were invested with an alumina-based, phosphate-bonded investment material. Both chambers of the casting machine were evacuated to 6 x 10(-2) torr; the argon pressure difference was then adjusted to either 50, 150, 300, or 450 torr. The porosity of the cast specimens was determined by x-ray radiography and quantitative image analysis. Tensile strength and elongation were measured by means of a universal testing machine at a strain rate of 1.7 x 10(-4)/s. The fractured surfaces were examined by SEM. Changes in Vickers hardness with depth from the cast surface were measured on polished cross-sections of the specimens. Raising the argon pressure difference to 300 and 450 torr caused a significant increase in internal porosity and a resultant decrease in the engineering tensile strength and elongation. The highest tensile strength (approximately 540 MPa), elongation (approximately 10%), bulk hardness (HV50g 209), and lowest porosity level (approximately 0.8%) occurred in the specimens cast at 150 torr. Turbulence of the metal during casting was thought to be responsible for the increase in porosity levels with the increase in argon pressure difference. By choosing an argon pressure difference (around 150 torr) suitable for this geometry, we could produce castings which have adequate mechanical properties and low porosity levels.
在使用两腔铸造机铸造钛时，赫勒等人（1993年）报告称，熔化腔与模具腔之间的压力差会影响铸件的质量。本研究检验了这样一个假设：压力差异会产生具有不同孔隙率和不同力学性能值的铸件。用氧化铝基磷酸盐粘结包埋材料包埋塑料哑铃形模型。将铸造机的两个腔都抽真空至6×10⁻²托；然后将氩气压力差调整为50、150、300或450托。通过X射线照相和定量图像分析确定铸造试样的孔隙率。使用万能试验机以1.7×10⁻⁴/s的应变速率测量拉伸强度和伸长率。通过扫描电子显微镜检查断裂表面。在试样的抛光横截面上测量维氏硬度随距铸造表面深度的变化。将氩气压力差提高到300和450托会导致内部孔隙率显著增加，从而使工程拉伸强度和伸长率降低。在150托下铸造的试样具有最高的拉伸强度（约540兆帕）、伸长率（约10%）、整体硬度（HV50g 209）和最低的孔隙率水平（约0.8%）。铸造过程中金属的湍流被认为是孔隙率水平随氩气压力差增加而增加的原因。通过选择适合这种几何形状的氩气压力差（约150托），我们可以生产出具有足够力学性能和低孔隙率水平的铸件。
