*Article* **Bionic Repair of Thermal Fatigue Cracks in Ductile Iron by Laser Melting with Di**ff**erent Laser Parameters**

**Siyuan Ma 1,2, Ti Zhou 1,3,\*, Hong Zhou 1,2, Geng Chang 1,2, Benfeng Zhi 1,2 and Siyang Wang 1,2**


Received: 12 December 2019; Accepted: 3 January 2020; Published: 9 January 2020

**Abstract:** Nodular iron brake discs typically fail due to serious thermal fatigue cracking, and the presence of graphite complicates the repair of crack defects in ductile iron. This study presents a novel method for remanufacturing ductile iron brake discs based on coupled bionics to repair thermal fatigue cracks discontinuously using bio-inspired crack blocking units fabricated by laser remelting at various laser energy inputs. Then, the ultimate tensile force and thermal fatigue crack resistance of the obtained units were tested. The microhardness, microstructure, and phases of the units were characterized using a digital microhardness meter, optical microscopy, scanning electron microscopy, and X-ray diffraction. It was found that the units without defects positively impacted both the thermal fatigue resistance and tensile strength. The unit fabricated at a laser energy of 165.6+<sup>19</sup> −15 J/mm<sup>2</sup> had sufficient depth to fully close the crack, and exhibited superior anti-cracking and tensile properties. When the unit distance is 3 mm, the sample has excellent thermal fatigue resistance. In addition, the anti-crack mechanism of the units was analysed.

**Keywords:** laser remelting; ductile iron; bionic crack blocked unit; repair discontinuously; thermal fatigue crack
