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Manufacturers of heat treating and brazing vacuum furnaces and controls, complete hot zone and vacuum furnace retrofits, thermal spray coatings, plasma, HVOF and paint coating services.

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Archives for November 2014

Heat Treatment of Landing Gear

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The heat treatment of landing gear is a complex operation requiring precise control of time, temperature, and carbon control. Understanding the interaction of quenching, racking, and distortion contributes to reduced distortion and residual stress. Arguably, landing gear has perhaps the most stringent requirements for performance. They must perform under severe loading con­ditions and in many different envi­ronments. They have complex shapes and thick sections. Alloys used in these applications must have high strengths between 260 to 300 ksi (1,792 to 2,068 MPa) and excellent fracture toughness (up to100 ksi in.1/2, or 110 MPa×m0.5). To achieve these design and per­formance goals, heat treatments have been developed to extract the optimum performance for these alloys.

The alloys used for landing gear have remained relatively constant over the past several decades. Alloys like 300M and HP9-4-30, as well as the newer alloys AF-1410 and AerMet 100, are in use today on commercial and military aircraft. Newer alloys like Ferrium S53, a high-strength stainless steel alloy, have been proposed for landing gear applications. The alloy 300M (Timken Co., Canton, OH) is a low-alloy, vacuum-melted steel of very high strength. Essentially it is a modified AISI 4340 steel with silicon, vanadium, and slightly greater carbon and molybdenum content than 4340. The alloy is governed by standard AMS 6417. This alloy has a very good combination of strength (280 to 305 ksi, or 1,930 to 2,100 MPa), toughness, fatigue strength, and good ductility. It is a through hard­ening alloy to large thicknesses. . By D. Scott MacKenzie, Houghton International Inc. Valley Forge, PA

Looking after Mechanical Vacuum Pumps

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This article is written for vacuum pumps such as the oil sealed rotary piston pumps used on many heat treating and vacuum furnace applications. The same information would also apply to the oil diffusion holding pump if it is used. This pump may be either a vee belt driven pump or a direct drive pump. The holding pump is used to keep the oil diffusion pump evacuated below the critical backing pressure when the main pump is in roughing mode.

All mechanical vacuum pumps need maintenance and the pump manufacturer usually lists the basic checks needed in the pump operation manual. This will vary with the application that the pump is used on but, at a minimum, will include the following: check oil level daily or weekly, depending on the application and use, change oil and check the shaft seal area for leaks every 6 months and inspect the exhaust valves and gas ballast valve seals every 12 months.

Delineation and Measurement of Grain Size by EBSD

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Grain size measurement by electron backscattered diffraction (EBSD) has several unique advantages over the traditional measurement of etched specimens by the light optical microscopy (LOM) approach as defined in ASTM E 112. This is most evident when trying to measure the grain size of twinned face-centered cubic (FCC) metals where two major problems are encountered.

First, in many cases, it is difficult to reveal a very high percentage of the grain boundaries by etching. Secondly, nearly all etchants for twinned FCC metals do reveal the twin boundaries and one must ignore the twin boundaries when measuring the grain size by LOM. The notable exception to this experience is electrolytic etching of the 300 series of austenitic stainless steels where Bell and Sonon’s aqueous 60% nitric acid [1], using a platinum cathode and a voltage no greater than 1.5 V DC will reveal nearly 100% of the grain boundaries and virtually none of the twin boundaries. Another significant problem that affects EBSD results somewhat more than LOM etching results is the greater difficulty in preparing the highly ductile FCC metals to the perfection needed to get a very high percentage of the pixels to be indexable. Specimen preparation [2-4] is a very critical step in getting a very high percentage of indexable pixels in the field of view. This is not a trivial matter.