Effect of cadmium-free filler metal on mechanical properties and microstructure of PDC cutters
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摘要:
【目的】 PDC 钻头不仅是地质保障装备的重要组成部分， 更是推动煤炭行业技术进步和效率提升的关键工具。 针对目前 PDC 钻头采用含镉银钎料进行钎焊， 而镉是污染性毒性元素， 提出采用无镉环保钎料钎焊 PDC 钻头的新思路。 【方法】 从钎料与母材的润湿机制出发， 采用高银含 Sn、含 Mn、 Ni 和只含 Ni 的 Ag-Cu-Zn 系钎料对 PDC 切削齿和钢进行火焰钎焊。 分析了不同钎料的剪切强度和 PDC 切削齿的焊后性能。 对熔化温度最高的钎料焊前和焊后 PDC 切削齿进行微观形貌、 元素含量和拉曼光谱分析， 探究钎焊温度是否会对 PDC 切削齿造成热损伤。 在此基础上， 分析了钎缝界面组织形貌、 元素扩散情况、 焊后断面特征和物相组成， 阐述了无镉 Ag-Cu-Zn 系钎料钎缝形成机理。 同时测量并计算了钎料与两侧界面的润湿角和化学亲和力参数， 综合评价钎缝性能。 【结果和结论】 研究表明： (1)4 种无镉 Ag-Cu-Zn 系钎料均能满足 PDC 切削齿钎焊强度要求， 其中含 Mn、Ni 的 Ag-Cu-Zn 系钎料可获得 322.989 MPa 的强度值。 (2) 含 Sn 的 Ag-Cu-Zn 钎料钎缝形成机理是界面处元素的微扩散； 而含 Mn、 Ni 或只含 Ni 的 Ag-Cu-Zn 钎料钎缝形成机理是在界面处形成扩散层，增加了界面处的键合力。 (3) 含 3%Sn、 含 Mn、 Ni 和只含 Ni 的 Ag-Cu-Zn 系钎料为延性断口； 含5%Sn 的 Ag-Cu-Zn 系钎料为脆-韧混合断口。 (4)Mn 能降低两侧界面处富 Cu 相与母材的张力， 而 Ni只能降低钢界面处富 Cu 相的张力。 因此， 含 Mn、 Ni 的无镉 Ag-Cu-Zn 系钎料强度最高。 研究结果为环保型无镉钎料在 PDC 钻头钎焊方面的工程应用提供了理论和试验支撑， 有力推动了 PDC 钻头的钎焊技术向更加环保、 新型的方向转型升级。
Abstract:[Objective] PDC bits are critical components of geological support equipment and play a vital role in advancing technology and improving efficiency in the coal industry. Currently, PDC bits are brazed using silver filler metals containing cadmium, a toxic and polluting element. This study introduces the use of environmentally friendly, cadmiumfree filler metals for brazing PDC bits. The study investigates the wetting mechanism between brazing filler metals and base materials, utilizing Ag-Cu-Zn series brazing filler metals containing high silver and Sn, Mn and Ni, and only Ni for flame brazing of PDC cutters and steel. The shear strength of different brazing solders and the performance of PDC cutters post-welding were analyzed. Microstructure, element content, and Raman spectra of PDC cutters with the highest melting temperature were examined pre- and post-brazing to assess potential thermal damage. Interface morphology, element diffusion, section features, and phase composition of brazing joints were analyzed to elucidate the formation mechanism of cadmium-free Ag-Cu-Zn series filler metal joints. Additionally, the wetting angle and chemical affinity parameters of the filler metal and interfaces were measured and calculated to comprehensively evaluate brazing performance. The results indicate that: (1) All four cadmium-free Ag-Cu-Zn brazing alloys satisfy the strength requirements for PDC cutter brazing, with Ag-Cu-Zn brazing alloys containing Mn and Ni achieving a strength of 322.989 MPa. (2) The brazing mechanism of Ag-Cu-Zn solder containing Sn involves micro-diffusion of elements at the interface. For brazing joints containing Mn and Ni or only Ni, the formation mechanism involves creating a reaction layer at the interface, which increases bonding strength. (3) The fracture morphology of Ag-Cu-Zn series brazing metal containing 3% Sn, Mn and Ni, and only Ni is ductile fracture, while the Ag-Cu-Zn series brazing alloy containing 5% Sn exhibits a brittleductile mixed fracture. (4) Mn reduces the tension between the Cu-rich phase and the base metal on both sides of the interface, whereas Ni only reduces the tension at the steel interface. Consequently, cadmium-free Ag-Cu-Zn brazing joints containing Mn and Ni have the highest strength. These findings provide theoretical and experimental support for the engineering application of environmentally friendly cadmium-free brazing filler metals in PDC bit brazing, promoting a transition towards more sustainable and advanced brazing technologies.
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Keywords:
- cadmium-free filler metal /
- PDC cutters /
- mechanical properties /
- microstructure /
- chemical affinity
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