Microstructure,Properties and Crack Suppression Mechanism of High-speed Steel Fabricated by Selective Laser Melting at Different Process Parameters

To enrich material types applied to additive manufacturing and enlarge application scope of additive manufacturing in conformal cooling tools,M2 high-speed steel specimens were fabricated by selective laser melting(SLM).Effects of SLM parameters on the microstructure and mechanical properties of M2 high-speed steel were investigated.The results showed that substrate temperature and energy density had significant influence on the densification process of materials and defects control.Models to evaluate the effect of substrate temperature and energy density on hardness were studied.The optimized process parameters,laser power,scan speed,scan distance,and substrate temperature,for fabricated M2 are 220 W,960 mm/s,0.06 mm,and 200℃,respectively.Based on this,the hardness and tensile strength reached 60 HRC and 1000 MPa,respectively.Interlaminar crack formation and suppression mechanism and the relationship between temperature gradient and thermal stress were illustrated.The inhibition effect of substrate temperature on the cracks generated by residual stresses was also explained.AM showed great application potential in the field of special conformal cooling cutting tool preparation.

MFI/MEL分子筛催化甲醇制烯烃反应关键参数的集成方法

了解与关键催化性能参数(如选择性和稳定性)相关的催化剂特性对于合理设计催化剂是非常重要的.本文重点考察了甲醇制烯烃(MTO)过程中MFI、MEL及其共生沸石分子筛的催化行为和构效关系.表征结果表明,丙烯和丁烯的高产率和MeOH的高转化率均与Pentasil分子筛结构中晶格Al位的富集相关,这也被27Al MAS NMR结果和3-甲基戊烷裂解结果证实.催化剂对MTO反应的催化性能与其晶体尺寸、外部B酸中心和铝配对等性质之间缺乏相关性,表明它们对提高丙烯选择性的作用不大.本文分析表明,催化剂失活非常复杂,受交叉点处晶格铝富集、总铝含量和晶体尺寸影响较大,且MFI和MEL相共生加速了催化剂失活.

雷暴冲击风作用下风力发电机动力响应参数

为了研究移动雷暴冲击风的时域特征及其作用下风力发电机动力响应参数的特点,利用谐波叠加法模拟得到移动雷暴冲击风的风速时程;建立考虑叶片和塔筒耦合作用的风机结构有限元模型,得到沿塔筒高度方向加速度、位移、截面应力、剪力的响应分布规律;考虑风机停机状态下不同叶片的停摆角度,进一步分析叶片及塔筒的加速度、位移响应;考虑不同风向角对风机影响,分析动力响应的频域特性,给出振型参与系数、塔顶位移及加速度和塔底弯矩的幅值随频率的变化规律。研究表明,移动雷暴冲击风的风速时程包括2个明显的波峰(0~T/3、T/3~T/2),不同叶片停摆角下位移响应峰值的变化与所在位置高度密切相关,雷暴冲击风荷载频率和一阶主频(0.230 Hz左右)对结构位移和截面弯矩幅值影响明显。