Properties and Applications of Binder Treated Mixes as Alternatives to Diffusion Alloyed Grades. Candido Ruas and Ray Guo Quebec Metal Powders Limited

Transcription

1 Properties and Applications of Binder Treated Mixes as Alternatives to Diffusion Alloyed Grades Candido Ruas and Ray Guo Quebec Metal Powders Limited Keywords: Properties, Binder Treatment, Diffusion Alloyed Powder, Prealloyed Powders Abstract: A family of binder treated premixes, 40A, 40B, 44A & 44B, are introduced as lower cost alternatives to the diffusion alloyed powders. These premixes use a water atomized base powder, which is prealloyed with 0.5% or 0.85% Mo and mixed with nickel, copper and graphite. The mixes are subsequently treated with organic binders to prevent nickel, copper and graphite segregation and to improve the premix flow rate, thus resulting in characteristics similar to diffusion alloyed powders. The 40 and 44 line of products is used to manufacture a variety of automotive and other structural parts. Their compressibility, weight consistency, mechanical properties and microstructure were studied in comparison to mixes of diffusion alloyed powders containing 1.75% and 4.0% nickel. The binder treated mixes reproduced the dimensional change, consistency and mechanical properties of the diffusion alloyed grades at lower cost. Two case studies of successful applications are also presented. Introduction Diffusion bonding is a thermal treatment process, which creates superficial bonds between iron particles and alloying elements by high temperature diffusion in an annealing furnace. Figure 1(a) shows a nickel and copper particle, diffusion bonded to an iron particle. Alternatively, the superficial bonds can be achieved by polymeric adhesion using a binder treatment process in the blender, Figure 1(b). Although the two technologies involve very different routes in powder manufacturing, they have the same technical objectives of improving powder mix homogeneity, increasing flow and prevent dusting during powder handling, thus enhancing the stability, (a) (b) Figure 1. Micrographs of: (a) diffusion alloyed particle and (b) binder treated particle

2 particularly the dimensional stability, of the sintered products. Therefore, binder treated mixes can be considered as an alternative to the diffusion alloyed powders at lower cost. By using the patented binder treatment technology [1], QMP developed 44A and 44B in 1996, the first two press-ready mixes with diffusion bonded characteristics [2-4]. 40A, 40B, 44A and 44B A binder treatment technology,, was developed to produce press-ready mixes in order to improve powder mix homogeneity, flow rate and product consistency, as well as to reduce dusting during powder handling [5, 6]. To produce 40A and 40B, the % Mo prealloyed ATOMET4001 is used as the base powder, which is mixed with nickel, copper and graphite, followed by a binder treatment to produce a press-ready mix. 44A and 44B are complementary mixes that are based on ATOMET 4401, a prealloy of 0.85% Mo. The higher molybdenum content compensates for the lower levels of copper and nickel compared to their and diffusion alloyed alternatives. mixes are formulated to reproduce the same dimensional changes and mechanical properties as the diffusion alloyed powder grades, FD0205 and FD0405 (MPIF Standard 35), respectively. Table 1 compares the various properties of the binder treated and the diffusion alloyed premixes. The apparent densities are very similar for all mixes, but the flow rate of the mixes are improved by 6 sec, which enhances the diefilling performance. The grades are equivalent in compressibility and green strength to their diffusion alloyed counterparts. For sintered properties, 44A & 44B show higher hardness, strength and similar impact energy, but slightly lower elongation than the diffusion alloyed powders. This is due to the solution hardening effect of the additional molybdenum. Summarizing the properties in Table 1, 44A and 44B can be used as drop-in substitutes for the diffusion alloyed grades with the exact same chemistry. Alternatively, 44A & 44B can also be used to meet the same application requirements but with a higher apparent hardness. By adjusting the mix formulation, 44A and 44B can reproduce the same dimensional changes as the diffusion alloyed mixes; hence they can be used as replacements for the diffusion alloyed powders without modifying existing dies. In recent years, the 44A and 44B have been used to replace the diffusion alloyed mixes in the production of parts for cars, power tools, appliances, business and agricultural machines, see Figure 2. In addition, part manufacturers have started to design new parts with 44A and 44B rather than the traditional diffusion bonded powders. Figure 2. Parts manufactured with 44A & 44B

3 Table 1. Properties of Mo-alloyed mixes versus diffusion alloyed powder. PROPERTY CHEMISTRY, (%) Mo Ni Cu Graphite Lubricant, EBS wax FD-0205 (MPIF) A A 1.75 FD-0405 (MPIF) B B 4.00 PHYSICAL Apparent density, g/cm 3 Flow rate, sec/50g COMPACTION Green density, g/cm 3 Compacting pressure, MPa Green strength, N/mm SINTERING* Sintered density, g/cm 3 Hardness, HRC Tensile strength, N/mm 2 Yield strength, N/mm 2 Elongation, % Impact energy, J * Sintered at 1120 o C, 25 min. in a 90N 2 /10H 2 atmosphere. Case Studies The following are two case studies in the successful commercial application of 44A as an alternative to the diffusion alloyed powder. Case 1 - Business Machine Parts Figure 3 shows one of the gears manufactured with 44A. This part is used in business machines and traditionally produced with the diffusion alloyed grade containing 1.5% Cu and 1.75% Ni. To qualify 44A for the gears, parallel tests were carried out between 44A and diffusion bonded FD The gears were pressed to a green density of g/cm 3 for both 44A and FD-0205 materials, and then sintered at 1125 C for 30 min. in a mesh belt type furnace with an endothermic atmosphere. Subsequently, the gears were heattreated and tempered. The green, sintered and heat-treated properties are listed in Table 2. 44A showed very similar sintered and heat-treated properties relative to the diffuson bonded FD-0205 in terms of the hardness, crush load and dimensional change. The dimensional stability of 44A was well controlled with a variation of mm in the outer

4 Figure 3. Gear manufactured with 44A diameter, the same as or slightly better than that of FD A substantial saving of the material cost was achieved by using 44A for manufacturing these gears. Density, g/cm3 Table 2. Gear properties Case 1 Apparent Hardness Tooth Crush Load Kgf Outer diameter, mm Specification 6.8 min. HRC 30 min Material *FL-44A FD-0205 *FL-44A FD-0205 *FL-44A FD-0205 *FL-44A FD-0205 Green Min Max Sintered Min HRB 78 HRB Max HRB 83 HRB Heat Treated Min HRC 34 HRC Max HRC 37 HRC * 44A Case 2 - Synchronizer Hub A synchronizer hub, as shown in Figure 4, was being produced using diffusion bonded FD To reduce the material cost, a program was initiated to qualify the 44A as an alternative in manufacturing this automotive part used in small cars. The synchronizer hub weighs 250 grams and has a sintered density of g/cm3.

5 Figure 4. Synchronizer hub used in small cars As shown in Table 3, 44A was as compressible as the diffusion bonded FD-0205 and met the part specifications. 44A successfully reproduced the mechanical and dimensional properties of the diffusion bonded FD-0205 and qualified as a low cost drop-in alternative to the diffusion bonded material in manufacturing the synchronizer hubs. Table 3. Results of synchronizer hub CASE 2 Material Compacting pressure, tons Sintered Density *, g/cm3 Apparent Hardness, HRB Dimensional Change, % vs. Die Size Specification A FD * Sintering at 1120 C, endothermic atmosphere, mesh belt furnace with a belt speed of 145mm/sec. Conclusions Using binder treatment technology, mixes based on 0.5% or 0.85% Mo pre-alloyed atomized powder with additions of copper and nickel, can effectively replace the FD-0205 and FD-0405 diffusion alloyed grades. Moreover the 40A, 40B, 44A & 44B are lower cost alternatives to the diffusion bonded powders. The binder treated premixes, having much improved powder homogeneity, flow and dust resistance; result in physical characteristics that are similar to the diffusion bonded mixes. The alternatives have equivalent compaction properties and exhibit very similar sintered mechanical properties to the diffusion alloyed powders. 40A, 40B, 44A & 44B can be formulated to reproduce the same dimensional changes as their diffusion alloyed counterparts so that they can be used as drop-in replacements without the need to modify existing dies.

6 Since their introduction, 44A & 44B have been well received by part manufacturers and are used to make components for cars, power tools and household appliances as well as business and agricultural machinery. They have also been used as press-ready mixes for new part development, as well as replacements for the diffusion alloyed mixes. Acknowledgement My sincere thanks go to Mr. U. L. Yang of Trinity Metallize Co., Ltd., Taiwan, for his efforts in testing and qualifying 44A for the business machine parts and his permission to use the information in Case 1. References [1] F. Gosselin, Segregation-Free Metallurgical Powder Blends Using Polyvinyl Pyrrolidone Binder, U.S. Patent No. 5,069,714. [2] FLXD2774 (44B), a binder treated mixture of ATOMET 4401 with 1.20%Cu, 3.50%Ni and % graphite sent to Uni-Tech Metallurgy Co., Ltd., via Sydkenn Corporation, Taiwan, in November [3] FLXD2869 (44A), a binder treated mixture of ATOMET 4401 with 1.25 %Cu, % Ni and % graphite, and also FLXD2774 (44B), a binder treated mixture of ATOMET 4401 with 1.20% Cu, 3.5%Ni and % graphite, sent to Korea Powder Metallurgy Co. Ltd., Korea, in April [4] J. P. Poirier, 44: the original alternative to diffusion-bonded powder, QMP Notes, Quebec Metal Powders, Volume 10, No. 1, spring [5] F. Gosselin, M. Gagne and Y. Trudel, Segregation-Free Blends: Processing Parameters and Product Properties, Word Conference on Powder Metallurgy, The Institute of Metals, London, 1990, Vol. 1, pp [6] C. Gelinas, F. Chagnon and Y. Trudel, Optimizing Properties of Binder-Treated Ferrous Powder Premixes, Advances in powder Metallurgy & Particulate Materials, MPIF, Princeton, 1995, pp.3-45.