1、14FTM15 AGMA Technical Paper Application of a Unique Anti-wear Technology - Ion-Sulfurized Lubricating Gradient Material By G. Wang, Sam Metallurgical and Materials Solutions, LLC, Y. Zhang, X. Zhang, and H. Liu, Shanghai Pioneering Surface Material Co. Ltd.2 14FTM15 Application of a Unique Anti-wea
2、r Technology - Ion-Sulfurized Lubricating Gradient Material Gordon Wang, Sam Metallurgical and Materials Solutions, LLC, Yifei Zhang, Xinhui Zhang, and Hua Liu, Shanghai Pioneering Surface Material Co. Ltd. The statements and opinions contained herein are those of the author and should not be constr
3、ued as an official action or opinion of the American Gear Manufacturers Association. Abstract Ion-sulfurized lubricating gradient material (LGM), is a state-of-the-art technology conferring excellent anti-friction and wear-resistant characteristics on metallic parts including gears, splines, and bea
4、rings. It is characterized by a sulfur-proliferated zone composed of sulfides and sulfur-metal solid solution case with smooth sulfur compositional gradient inside the underlying bulk. A variety of metals and alloys, including steels, cast irons, super-hard alloys, and bronze, are suitable for ion-s
5、ulfurization. This treatment is carried out at low temperature; therefore, geometric integrity, microstructure and mechanical properties of the bulk are not compromised. It provides excellent solid lubrication which increases power efficiency and inhibits adhesive wear, seizure and scuffing in gears
6、. Moreover, the micro-porous morphology in LGMs surface accommodates lubricating additives. It improves run-in efficiency of machinery/automotive units. The contact fatigue in gears and splines is noticeably reduced. The tribological property of the LGM layer on steel parts can survive an extraordin
7、arily high temperature, which is rarely surpassed by other processes. With LGM, carbon/alloy steels can be used to substitute for certain copper alloys in manufacturing specific gears. It fulfills the requirement for maintaining stronger bulk while achieving superior friction/adhesion/run-in charact
8、eristics. In this article, the engineering characteristics of LGM technology are introduced, and exemplary applications are presented. Copyright 2014 American Gear Manufacturers Association 1001 N. Fairfax Street, Suite 500 Alexandria, Virginia 22314 October 2014 ISBN: 978-1-61481-107-7 3 14FTM15 Ap
9、plication of a Unique Anti-wear Technology - Ion-Sulfurized Lubricating Gradient Material Gordon Wang, Sam Metallurgical and Materials Solutions, LLC, Yifei Zhang, Xinhui Zhang, and Hua Liu, Shanghai Pioneering Surface Material Co. Ltd. History of ion-sulfurized lubricating gradient material (LGM) t
10、echnology In modern industry, large fraction of machinery components, including gears, splines, and bearings, continually fall out of service because of wear and wear-related damages, along with which there is tremendous loss in raw materials, labor, and energy. Besides wear damages, friction consum
11、es huge power share and decreases power transferring efficiency. Lubricating oil and grease can fail at a variety of conditions, which sometimes cause severe accidents 1. Therefore, sound friction-reduction and wear-resistant technology is beneficial to economy, environment and safety. With such bac
12、kground, in 1980s, physicist Zhang Yifei developed the low-temperature physiochemical ion-sulfurization technology. In a vacuum environment, ionized sulfur diffuses into the metal, and a solid-lubricating case with composition gradient of sulfur is formed. Thus this technology is called ion-sulfuriz
13、ed lubricating gradient material (LGM) technology, or LGM technology, and the ion-sulfurization process is called LGM process. The LGM configuration is indicated in Figure 1, and the microscopic picture in cross section is shown in Figure 2. During the implementation and industrialization of this te
14、chnology, substantial engineering advantages have drawn a constantly increasing attention. Figure 1. Indicative configuration of lubricating gradient material (LGM) Figure 2. Microscopic picture of lubricating gradient material, 120 4 14FTM15 Characteristics of LGM Extraordinary tribological charact
15、eristics The sulfides formed in LGM process possess hexagonal lattice structure and extreme lattice anisotropy, which contributes to low friction coefficient 2. Owing to such characteristics, LGM technology increases power-transferring efficient and reduces friction heat. It also retards asperity we
16、lding and adhesive wear with insufficient or non-uniform lubricant, especially under high speed rolling and sliding condition. There are various surface processing mythologies that target acquiring advanced tribological properties on metallic parts, including physical or chemical depositing/bonding/
17、spraying, and chemical diffusion process, like carburization and nitriding 3, 4. LGM technology distinguished itself by forming a micro-porous friction-reduction layer. Due to its micro porous feature (Figure 3), the LGM layer provides myriads of micro-reservoirs for lubricant agent and ensures hydr
18、odynamic lubrication. Efficient lubrication alleviates seizure and galling and prevents premature failure. Furthermore, regular lubricants might fail under certain circumstances, such as chemical decay, emulsion instability, and foaming. Thus, solid lubrication effect of LGM layer functions as backu
19、p protection under unexpected lubricant deterioration. It is well recognized that high contact load in gears causes extreme-pressure malfunction in lubricant 5. The LGM layer, however, mitigates shear stress in lubricant and compensates for the insufficient extreme-pressure additives. Another notice
20、able engineering benefit of LGM is that it reduces run-in time, as it smoothes the parts surface via merging contact asperities. The LGM processed article maintains a solid lubricating and wear-resistant surface, either at elevated-temperature or in radiating environment. Ion-sulfurized LGM in steel
21、 is able to maintain its lubricating property at a temperature even higher than phase transformation temperature of steel, while conventional lubricating grease only works up to 300C (specific formula may survive a higher temperature), and molybdenum disulfides survive 315C under non-vacuum environm
22、ent 2. LGM technology is being utilized in steel molds/dies in forming aluminum parts, due to the chemically inert characteristics of the sulfide layer. Figure 4 indicates that less damage was induced from service of LGM processed tools. In regular dies, the chilling effect from the mold-releasing a
23、gents sets on hot fatigue cracks on surface. However, the sulfide layer allows for less amount of mold-release agent to be used, which inhibits the occurrence of this kind of cracks (Figure 5). Figure 3. Micro porous feature of LGMs sulfide layer 5 14FTM15 Figure 4. Surface characteristics of tool s
24、teel mold conveying high-pressure liquid aluminum to cast mode (left, conventionally processed, used for 9599 cycles, right, LGM processed, used for 40322 cycles) Figure 5. Surface defect identification in LGM processed bearing roller used in windmill power generator LGM process is also being applie
25、d in steel hot milling industry. The service life of LGM processed rolls, made of either alloy or cast iron, can increase by 50% 100%. Nondestructive inspection effect With LGM processing, the sharp geometric non-continuities on parts turn more readily visible via color contrast, which is the effect
26、 of sulfur plasma interacting with geometric edges. Such advantage can be specified to delineate surface cracks induced by heat treatment, forging, welding, hydrogen embrittlement, and grinding or hard turning. Therefore, open defects can be identified visually, as in conventional dye-penetration or
27、 magnetic-powder inspection. This approach helps avoid assembling flawed parts into machines or automobiles and reduces latent maintenance cost. One exemplary defect is shown in Figure 5. No distortion in LGM process LGM is formed at temperatures as low as 80C 200C, which is lower than the tempering
28、 temperature for most carbon and alloy steels. Thus, the microstructures of the substrate are not impaired. The process inflicts no geometric distortion, and the dimension variation is below 0.0005 mm. There is no need for finish grinding under most circumstances. 6 14FTM15 An environment-friendly t
29、echnology LGM is called a green technology, as very little hazardous emission and waste is released during the treatment. LGM extends parts service life and renders low-cost metals gain excellent tribological properties, which reduces cost in raw materials. As the friction coefficient plummets, powe
30、r and fuel consumption drops noticeably. Therefore, this technology is strategically advantageous since energy in one key-drive gear for the economy. With wear damage reduced, extra profit is garnered by reducing maintenance time and cost. Friction/wear test Friction and wear test was designed in a
31、manner that severe wear condition of bearing ball was simulated - the sliding of ball against steel ring. There was a remarkable reduction in friction coefficient and wear marks on LGM processed bearing rollers. Although this test was conducted on ball/ring pair for simplicity and expedition, analog
32、ous contributions of LGM can be observed in gears. Test machine, interface, and samples A universal vertical friction and wear test machine was used in friction/wear test. The indicative test setup is shown in Figure 6. In each relatively sliding pair, there are two parts, 6.35 mm bearing ball, and
33、54 mm steel ring. Friction/wear data of LGM processed pair was compared with regularly heat treated/carburized pair. The following list contains the primary test conditions: - Steel bearing ball (surface roughness Ra=0.8m: Fixed in disc clamp with one side sliding on the steel ring (surface roughnes
34、s Ra=1.6 m) - Force: 50N - Temperature: Room temperature - Shaft rotating rate: 100 RPM in run-in, 800 RPM as working rate - Time-span: 1 minute run-in at 100 RPM, and 21 minutes run at 800 RPM - Lubricant: # 32 lubricating oil (viscosity 2733mm2/S at 40C) - Figure 6. Indicative configuration of fri
35、ction and wear test machine Key 1 Holder 2 Large test ring (AISI 4118) 3 6.35 mm - diameter steel ball (AISI 52100) 4 - Disc clamp, unit: mm 7 14FTM15 Specimens preparation Two wear couples of bearing ball and steel ring were used, one pair was conventionally heat treated, and the other was LGM proc
36、essed after conventional heat treatment. I. Regularly processed parts 6.35 mm bearing ball: AISI 52100, heat treated (quenched and tempered). 54 mm steel ring: AISI 4118, carburized. Heat treatment for AISI 52100 bearing ball: Austenitize - oil quench - cryogenic treat - temper to hardness HRC62-64.
37、 Heat treatment for AISI 4118 ring: Carburize - double quench - temper Case depth: 1.1-1.2mm, hardness HRC 54-56. II. LGM processed parts 6.35 mm bearing ball: AISI 52100, heat treated (quenched and tempered), and LGM processed. 54 mm steel ring: AISI 4118, carburized, quenched and tempered, and LGM
38、 processed. Wear inspection Macro wear-marks were inspected with SLR camera, and micro wear marks were characterized with optical metallography. Test results Tests indicate that on LGM processed parts, friction coefficient decreased by 30%, wear mark area dropped by 80%. Figures 7 and 8 demonstrate
39、the friction coefficient data on regular wear couple composed of heat treated ball and carburized ring. While Figures 9 and 10 show the friction coefficient on LGM processed test parts, it can be observed that LGM drastically reduces friction coefficient and force, and the peak values, which is high
40、ly correlated with improved run-in efficiency and reduced wear damages. Figures 7 and 9 indicate that LGM decreases heat build-up rate. Figures 11 through 14 present the comparison of wear marks on LGM processed parts with regularly heat treated and carburized parts. The wear mark morphology in the
41、former is much less ridged. Figure 7. Friction coefficient - temperature - time curve of 6.35 mm bearing ball (AISI 52100, heat treated) vs. 54 mm steel ring (AISI 4118, carburized) 8 14FTM15 Figure 8. Friction coefficient - force - time curve of 6.35 mm bearing ball (AISI 52100, heat treated) vs. 5
42、4 mm steel ring (AISI 4118, carburized) Figure 9. Friction coefficient - temperature - time curve of 6.35mm bearing ball (AISI 52100, heat treated and ion-sulfurized) with steel ring (AISI 4118, carburized and LGM processed) Figure 10. Friction coefficient - force - time curve of 6.35mm bearing ball
43、 (AISI 52100, heat treated and ion-sulfurized) with steel ring (AISI 4118, carburized and LGM processed) 9 14FTM15 Figure 11. Microscopic picture of wear marks on heat treated bearing ball, 120 Figure 12. Microscopic picture of wear marks on heat treated and LGM processed bearing ball, 120 Figure 13
44、. Microscopic picture of wear marks on carburized ring, 120 10 14FTM15 Figure 14. Microscopic picture of wear marks on carburized and LGM processed ring, 120 Application of LGM in gears and beyond Conventional bulk heat treatments and surface treatments, including but not limited to quenching/temper
45、ing, carburizing, nitriding and other thermochemical processes, having being used to gain friction and wear resistance 3. Following heat treatment, and carburization or nitriding, which forms a microstructure with hardness, rigidity, and contact and flexural strength several times higher than brass,
46、 the gears/bearings can be further LGM processed, which greatly extends and upgrades the tribological property by superimposing a self-lubricating layer. Table 1 shows the benefit of LGM in friction coefficient with respect of nitriding process. The low-interaction LGM layer prohibits adhesive wear,
47、 which was considered as the most universal and least preventive form of wear 4. The solid-lubricating effect also attenuates shear stress in the contact surface. Furthermore, the LGM technology improves marvelously the fatigue property, as to be described below. Because of those highlights, the sub
48、stitution of LGM processed steel bears for counterparts made of copper alloys turns strategically valuable, and overcomes such drawbacks as low contact and flexure strength, hardness, toughness and rigidity. Furthermore, because of high strength and toughness of steels, the load-transferring unit ca
49、n be more compact and precise. The high cost of copper also favors this tentative approach. Table 1 indicates that in LGM processed parts, friction coefficient drops by 1024%, compared to parts that were nitrided only. Friction temperature drops by 28% as well. Even without lubricant additive, parts with LGM are superior to regular counterparts in friction characteristics. Table 1. Indicative friction test comparison on nitrided part and nitrided/LGM processed part, under same lubricating condition (#32 lubricating oil
