Advanced Materials & Processes

NOV-DEC 2013

Covers developments in engineering materials selection, processing, fabrication, testing/characterization, materials engineering trends, and emerging technologies, industrial and consumer applications, as well as business and management trends

Issue link: http://amp.digitaledition.asminternational.org/i/211830

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Friction coefficient 1 0.8 600 0.6 500 Friction coefficient (c) 0.4 0.8 HT90820A coating 2B 5-in. diameter pin 0.6 1N Load, 26.68 mm WT diameter, 100 cm/s 650°C 600 500 0.4 400 0.2 300 0 0 200 400 600 800 1 200 1000 1200 1400 1600 1800 2000 Distance, m 700 0.8 HT90820B coating 2B 5.5-in. diameter pin 0.6 1N Load, 26.68 mm WT diameter, 100 cm/s 650°C 600 0.4 400 0.2 300 0 0 200 400 600 800 (d) 66 Fig. 3 — Wear resistance of (a) substrate, (b) CrC-NiCr + 5% (CaF2 + BaF2), (c) CrC-NiCr + 5% (CaF2 + BaF2 + Ag), and (d) NASA PS 304 coating. 700 400 HT90818A substrate 5-in. diameter pin 300 0.2 1N Load, 26.68 mm WT diameter, 100 cm/s 650°C 200 0 0 200 400 600 800 1000 1200 1400 1600 1800 2000 Distance, m (b) 700 1 Friction coefficient 6 (a) Friction coefficient i T S S e 1 200 1000 1200 1400 1600 1800 2000 Distance, m 700 HT91029A PS304 flat and 5-in. pin 1N Load, 34 mm WT diameter, 98 cm/s 650°C 0.8 0.6 500 600 500 0.4 400 0.2 300 0 0 200 400 600 800 200 1000 1200 1400 1600 1800 2000 Distance, m Figure 2 shows the microstructure details of Triboglide coatings with and without silver addition, along with the microstructures for PS 304 coatings. PS 304 is a NASA-developed self-lubricating composite coating based on a nichrome (80% Ni and 20% Cr by weight) binder and hard chrome oxide (Cr2O3) wear-resistant phase, with the addition of silver and eutectic BaF2/CaF2 as low- and high-temperature solid lubricants, respectively. The coating seems to possess a unique microstructure with lamellar structure and interfacial defects. It also shows a wide distribution of the metallic component within the oxide matrix. The new blend of proprietary HVOF Triboglide CrCNiCr-based coatings show good adhesion and hardness. Two coatings with and without silver, deposited by the HVOF process, were sent out to Argonne National Laboratory, Lemont, Ill., for high temperature wear testing. Results are shown in Figs. 4-6. Wear data in Fig. 3(a) shows that the friction coefficient of the uncoated bare substrate is 0.6, whereas with the coating it is reduced to ~0.3. Comparing the CrC-NiCr + 5% (CaF2 + BaF2) coatings with and without silver shows that adding silver deteriorates the overall high temperature wear behavior of the coating [Fig. 3(c)]. The heavy noise indicates adhesive galling at the initial stages and at the end of the pin on ADVANCED MATERIALS & PROCESSES • NOVEMBER-DECEMBER 2013

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