简介概要

添加铌和钼对Nimonic 80A合金激光硼化表面显微组织和磨损行为的影响

来源期刊:中国有色金属学报(英文版)2019年第2期

论文作者:N. MAKUCH P. DZIARSKI M. KULKA A. PIASECKI M. TULINSKI R. MAJCHROWSKI

文章页码:322 - 337

关键词:激光合金化;表面形貌;磨损测试;表面分析;磨损机制;镍基合金

Key words:laser alloying; surface topography; wear testing; surface analysis; wear mechanism; nickel alloy

摘    要:在Nimonic 80A合金表面用激光合金法技术制备较厚的表层。 激光表面改性前在材料表面预涂覆3种浆料:非晶硼、非晶硼与钼和非晶硼与铌。详细研究激光处理后表层的显微组织、硬度和耐磨性能。重熔区不同类型硼化物的形成与浆料成分有关,其硬度增加,可达HV 1000左右。通过计算样品和对磨件的质量磨损强度因子Imw和相对质量损失来评价样品的耐磨性。采用三维干涉显微镜、扫描电镜和电子能谱仪表征摩擦副的磨损行为。与未处理的Nimonic 80A合金相比,激光处理后的合金其耐磨性明显提高。含硼和铌的Nimonic 80A 合金激光合金化后的表面具有最低的质量损失强度因子(Imw=1.234 mg/(cm2·h))。激光合金化表层的沟槽清晰可见,其磨损机制为磨粒磨损。经激光处理后含硼和铌合金表面的能谱分析图谱中有氧存在,表现出额外的氧化磨损机制。

Abstract: Laser alloying was used for production of thick layers on surface of Nimonic 80A-alloy. For laser surface modification, three types of pre-coated pastes were applied: with amorphous boron, with amorphous boron and molybdenum as well as with amorphous boron and niobium. The microstructure, hardness and wear resistance of produced layers were studied in details. The presence of different types of borides in re-melted zone depended on the paste composition and caused an increase in hardness up to about HV 1000. The wear resistance was evaluated by calculation of mass wear intensity factor Imw and relative mass loss of specimen and counter-specimen. The wear behavior of the tested frictional pairs was determined by 3D interference microscopy, scanning electron microscopy equipped with EDS microanalyzer. The significant increase in abrasive wear resistance was observed in comparison to untreated Nimonic 80A-alloy. The lowest mass loss intensity factor was characteristic of laser-alloyed Nimonic 80A-alloy with boron and niobium (Imw=1.234 mg/(cm2·h)). Laser alloyed-layers indicated abrasive wear mechanism with clearly visible grooves. Laser alloying with boron and niobium resulted in the additional oxidative wear mechanism. In this case, EDS patterns revealed presence of oxygen on the worn surface of specimen.



详情信息展示

Trans. Nonferrous Met. Soc. China 29(2019) 322-337

Influence of niobium and molybdenum addition on microstructure and wear behavior of laser-borided layers produced on Nimonic 80A-alloy

N. MAKUCH1, P. DZIARSKI1, M. KULKA1, A. PIASECKI1, M. TULINSKI1, R. MAJCHROWSKI2

1. Institute of Materials Science and Engineering, Poznan University of Technology, Pl. M. Sklodowskiej-Curie 5, 60-965 Poznan, Poland;

2. Institute of Mechanical Technology, Poznan University of Technology, Pl. M. Sklodowskiej-Curie 5, 60-965 Poznan, Poland

Received 29 March 2018; accepted 23 August 2018

Abstract: Laser alloying was used for production of thick layers on surface of Nimonic 80A-alloy. For laser surface modification, three types of pre-coated pastes were applied: with amorphous boron, with amorphous boron and molybdenum as well as with amorphous boron and niobium. The microstructure, hardness and wear resistance of produced layers were studied in details. The presence of different types of borides in re-melted zone depended on the paste composition and caused an increase in hardness up to about HV 1000. The wear resistance was evaluated by calculation of mass wear intensity factor Imw and relative mass loss of specimen and counter-specimen. The wear behavior of the tested frictional pairs was determined by 3D interference microscopy, scanning electron microscopy equipped with EDS microanalyzer. The significant increase in abrasive wear resistance was observed in comparison to untreated Nimonic 80A-alloy. The lowest mass loss intensity factor was characteristic of laser-alloyed Nimonic 80A-alloy with boron and niobium (Imw=1.234 mg/(cm2·h)). Laser alloyed-layers indicated abrasive wear mechanism with clearly visible grooves. Laser alloying with boron and niobium resulted in the additional oxidative wear mechanism. In this case, EDS patterns revealed presence of oxygen on the worn surface of specimen.

Key words: laser alloying; surface topography; wear testing; surface analysis; wear mechanism; nickel alloy

1 Introduction

Nickel alloys are one of the most important classes of engineering materials due to their advantageous properties, e.g. high corrosion resistance and heat resistance. Unfortunately, the main disadvantage of these materials is poor wear resistance that limits their applications. Wear is recognized as the phenomenon of material removal from a surface due to interaction with a mating surface. Almost all the machine components lose their durability and reliability due to the intensive wear. The tribological wear is the process of destruction and removal of material from the surface of solids. This phenomenon is caused by the friction, and manifested by a continuous change of dimensions and shapes of the frictional pair. The causes of wear are in most cases of a mechanical character, less often mechanical, combined with the chemical interaction of the surrounding medium [1]. The possibilities of application of some materials are reduced because of wear problems. Therefore, the protection against wear becomes a primary concern of surface engineering [2]. The formation of hard surface layers can improve the wear resistance of materials. Especially, the surface layers, containing borides, carbides or nitrides, provide the wear protection of substrate material.

Laser surface alloying (LSA) became one of the most developed methods for thermo-chemical treatment of metals and alloys. During LSA, the alloying elements (metallic and non-metallic elements, carbides, oxides, nitrides etc.) are mixed with substrate material. The intensive melting and mixing of the materials take place in a molten pool due to convective, gravitational movement, hydrostatic pressure and vapor pressure generated as a result of the laser beam interaction with treated material [3]. Laser surface alloying involves high heating/cooling rates and gradients which produce metastable phases, leading to the development of a wide variety of microstructures with novel properties that cannot be produced by any conventional processing techniques. By the laser alloying the surface layer of the treated material, it is possible to obtain a fine-grained microstructure. Laser surface alloying (LSA) consists of simultaneous melting and mixing of the alloying elements and the alloyed material (substrate material). The aim of laser alloying is the saturation of treated material with alloying elements. The obtained microstructure, chemical composition, and physical as well as mechanical properties of the laser-alloyed layer are different than those of the substrate material or the alloying material. First of all, the laser-alloyed layer does not exhibit the characteristic layer structure, typical of diffusion processes. The intensive mixing of the alloyed and alloying materials takes place in the molten pool, therefore, there are no transitions from phases with a higher content of the alloying element to phases with lower content. All of phases in the laser-alloyed layer are uniformly distributed along its entire depth. The laser-alloyed layer, rich in alloying components, usually exhibits a higher hardness than the substrate, a higher fatigue strength, better tribological and corrosion properties, but at the same time with poorer smoothness of the surface in comparison with the condition prior to alloying [1]. However, these properties depend to a very high degree on the uniformity of mixing of the alloy in the molten phase, which, in turn, depends on the laser treatment parameters used.

Laser surface alloying was applied in order to improve wear resistance (increase in microhardness, decrease in the coefficient of friction) of different alloys: steels [4-6], titanium alloys [7-11], aluminum alloys [12-14] or copper alloys [15]. In recent years, the laser technology was intensively developed in order to produce thick, hard and wear resistant surface layers on nickel and its alloys [16-25]. In Ref. [16], the hardness and wear resistance of Hastelloy G-alloy were improved by producing of nitride layers. Laser gas-assisted nitriding was carried out using a molecular CO2 laser. This process resulted in the formation of a uniform nitride layer which was characterized by a thickness of 40 μm and good quality (cracks-free and without porosity). The presence of nitrides (Fe4N and CrN) caused the increase in hardness up to HV 350 in comparison with substrate material (HV 270). Laser alloying of Inconel 600-alloy with boron resulted in the formation of hardened layer [23]. The laser-borided layers were very thick (346-467 μm depending on the power of the laser beam used) and consisted of nickel, chromium and iron borides and Ni-Cr-Fe matrix (re-melted substrate). The presence of varying types of borides caused an increase in the hardness up to HV 1560. The wear resistance of laser-borided layer was significantly improved in comparison with the untreated Inconel 600-alloy. The laser surface alloying with Si and Al was proposed in order to improve oxidation resistance of Nimonic 80-alloy [19,20]. Laser surface modification of Inconel 625-alloy with TiC and WC particles was also examined [21]. It was found that laser alloying caused a decrease in corrosion resistance, because of the formation of galvanic micro-cells. The laser alloying with boron and niobium was used for the formation of composite boride layer on Nimonic 80A-alloy [24]. The presence of nickel, chromium and niobium borides caused the increase in microhardness up to HV 1000. The produced layers were characterized by ten times higher wear resistance in comparison with untreated Nimonic 80A-alloy.

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