氮化硼对电火花强化钛合金强化层的影响

Effect of BN on the strengthened layer of titanium alloy by EDM surface strengthening

为探究氮化硼对钛合金强化层组织与性能的影响,通过在准干式工作介质中混入单一粉末BN及混合粉末BN+Al,采用混粉准干式电火花表面强化技术对TC4钛合金进行表面强化。对不同强化工艺参数下的强化层微观组织形貌、裂纹分布、表面粗糙度及显微硬度等进行分析。结果表明:2种粉末条件下生成的强化层微观组织形貌均呈放射型花瓣状,且裂纹在强化层表面具有类似的分布特点,但BN+Al粉末条件下获得的强化层更加平整致密,且裂纹数量及延展长度都明显下降;强化层表面显微硬度较原始TC4钛合金相比均有大幅提高,当峰值电流为8.2 A时,添加BN和BN+Al的2种粉末条件下获得的强化层显微硬度分别达到1695.2 HV和1722.4 HV。混合粉末BN+Al介质下获得的强化层微观形貌比单一粉末BN条件下获得的强化层微观形貌更加平整致密,微裂纹的数量和延展长度明显减少。

To explore the effect of BN on the microstructure and properties of the strengthened layer,the surface of TC4 alloy is strengthened by mixing single powder BN and mixed powder BN+Al in the near-dry medium.The micro-structure,crack distribution,surface roughness and micro-hardness of the strengthened layers are analyzed using different strengthening process parameters.The results indicate that the microstructure of the strengthened layer under both powder conditions is radially petal-shaped,and the cracks have similar distribution patterns on the surface of the strengthened layer,but the enhanced layer obtained by BN+Al powder is more flat and compact,and the number of cracks and the extension length are significantly reduced.Compared with that of the original TC4 titanium alloy,the micro-hardness of the strengthened layer is significantly increased.The micro-hardness of the strengthened layer obtained with BN and BN+Al powders reaches 1695.2 HV and 1722.4 HV respectively at a peak current of 8.2 A.The micromorphology of the strengthened layer obtained under mixed powder BN+Al medium is flatter and more compact than that obtained under the condition of single powder BN,and the number and length of microcracks are significantly reduced.