钛粉末注射成形PEG/PMMA黏结剂体系的PHB改性研究

PHB-modification in PEG/PMMA binder for improving titanium powder injection molding process

金属注射成型(MIM)中使用水溶性聚乙二醇(PEG)和聚甲基丙烯酸甲酯(PMMA)黏结剂体系会导致大量孔洞形成,该黏结剂体系导热性差,使得零件尺寸越大,注射脱模时间越长。用聚(β-羟基丁酸酯)(PHB)作为PEG结晶抑制剂可解决上述问题。采用导热系数仪、DSC、流变学实验、傅里叶变换红外光谱(FTIR)等,研究PHB含量对黏结剂导热系数、结晶行为、喂料流变特性、注射保压时间及生坯显微结构的影响。结果表明:PHB/PEG共混物随着PHB含量的增加,结晶温度从纯PEG的55.18℃下降至25%(质量分数,下同)PHB改性的51.4℃,熔融焓从79.5 J/g逐渐增加至107.6J/g,导热系数从0.2433 W·m^(-1)·K^(-1)适当增加至0.3469 W·m^(-1)·K^(-1),黏结剂结晶度的增加可改善其导热性能;由于PEG/PHB/PVAc三元体系中存在复杂氢键的相互作用,导致黏结剂结晶温度从未添加PHB的50.07℃降低并稳定在添加25%PHB的43.3℃;添加15%PHB后制备的喂料黏度与剪切速率符合幂律流体规律,在120℃时喂料的剪切稀化指数从未改性的0.77减小至0.62,相同注射条件下注射脱模时间从未改性的100 s缩短至50 s便可获得表面光滑无裂纹、内部孔洞少且分布均匀的钛注射生坯。

During metal injection molding(MIM), water-soluble polyethylene glycol(PEG) and polymethyl methacrylate(PMMA) binder system usually lead to the formation of a large number of holes.The time spent in injection demolding increases with the size increasing of the parts for the poor thermal conductivity of the binder system. Poly(β-hydroxybutyrate)(PHB) was used as a PEG crystallization inhibitor to solve this problem. The effects of PHB content on the thermal conductivity, crystallization behavior, rheological properties of the binder, injection holding time and microstructure of the green body were studied by thermal conductivity meter, DSC, rheological experiments and fourier transform infrared spectroscopy(FTIR). The results show that in PHB/PEG blends, with the increase of PHB content, the crystallization temperature decreases from 55. 18 ℃ (pure PEG) to 51. 4 ℃ (25% PHB modified,mass fraction, the same as below). With the increase of PHB content from 0%-25%, the melting enthalpy and thermal conductivity of PEG blends gradually increase from 79. 5 J/g to 107. 6 J/g and from 0. 2433 W·m^(-1)·K^(-1) to 0. 3469 W·m^(-1)·K^(-1), respectively. The increasing of binder crystallinity leads to the improvement of thermal conductivity. Due to the complex hydrogen bond interaction in the PEG/PHB/PVAc ternary system, the crystallization temperature of the binder decreases from 50. 07 ℃ of pure PEG to 43. 3 ℃ of PEG with 25% PHB. The relationship between the viscosity and shear rate of the feedstock prepared with 15% PHB modified PEG binder conforms to the law of power-law fluid. And the shear thinning index of the feedstock prepared with 15% PHB modified PEG binder decreases from 0. 77 of pure PEG to 0. 62 at 120 ℃. Under the same injection conditions, the injection demolding time is significantly shortened from 100 s(unmodified) to 50 s of PEG with 15% PHB. Meanwhile, the injection green body, with smooth surface, few and uniform distribution internal holes can be obtained using 15% PHB modified PEG binder.