Cooling Indentation

Two pieces of work-hardened 5000 series aluminium alloy plate were butt welded together by arc welding. After the weld had cooled to room temperature, a series of hardness measurements was made on the surface of the fabrication. Sketch the variation in hardness as the position of the hardness indenter passes across the weld from one plate to the other. Account for the form of the hardness profile, and indicate its practical consequences. 

The apparatus consists of a 3-1. three-necked round-bottomed creased flask, with standard ball joints and an indented cone-shaped bottom (Note 1), which is heated by means of an electric mantle and is equipped with a high-speecT stirrer of stainless steel driven by a 10,000 r.p.m. motor (Note 2). One side neck is fitted with a bulb-type air-cooled condenser (Note 3), on top of which fits a 1-1. pressure-equalizing Hershberg dropping funnel (Note 4). The top of the dropping funnel is to be connected in turn to a U-tube containing a 1-cm. head of mercury. The entire apparatus is securely fastened to a sturdy support. 

In a 300-ml. Claisen flask, whose side neck is elongated by a 10-cm. indented section, 102 g. (1 mole) of acetic anhydride and 0.1 ml. (Note 1) of concentrated sulfuric acid are mixed by hand swirling. The mixture is cooled to 10° by swirling in an ice bath, then there is added, during about 10 minutes, 96 g. (1 mole) of recently distilled furfural (Note 2). The temperature is maintained at 10-20°. After addition is complete and the contents of the flask have been well mixed by swirling, the cooling bath is removed and the reaction allowed to warm up spontaneously. A maximum temperature of about 35° is usually reached in about 5 minutes. After the temperature has dropped to that of the room (20-30 minutes), 0.4 g. (Note 1) of anhydrous sodium... 

A. N,N-Diethyl-2,2,2-trichloroacetamide. A 1-1. three-necked flask equipped with a stirrer and dropping funnel is charged with 73 g. (1.00 mole) of diethylamine, 500 ml. of ether, and a solution of 40 g. (1.00 mole) of sodium hydroxide in 160 ml. of water. The mixture is stirred and maintained at a temperature of —10° to — 15° by a bath of Dry Ice and acetone while 200 g. (1.10 moles) of trichloroacetyl chloride is added in the course of 1 hour. The cooling bath is removed, the temperature is allowed to rise to 10°, and the organic layer is separated. The aqueous layer is extracted with two 50-ml. portions of ether. The ether extracts are combined, washed with 50 ml. of 5% hydrochloric acid, two 50-ml. portions of 5% sodium bicarbonate solution, and 50 ml. of water, and dried over magnesium sulfate. The ether is removed by distillation at atmospheric pressure. The residue is distilled through a short indented Claisen still head at reduced pressure. N,N-Diethyl-2,2,2-trichloroacetamide is collected at 77-79°/1.5 mm. 1.4902-1.4912 weight 183-200 g. (84-92%). 

A. Itaconic Anhydride A 500-cc. Pyrex Kjeldahl flask is fitted with an outlet tube 12 mm. in diameter bent for downward distillation. It is attached to a 100-cm. water-cooled condenser having an indented Pyrex inner tube (Note 1). Two 250-cc. long-neck distilling flasks are used in series as receivers, the vapors being led to the center of each flask by means of an adapter and glass tubing. Both receivers are cooled in a mixture of ice and water. 

The contents of the three receivers are combined and distilled at atmospheric pressure through a 15-cm. indented Claisen-type still head the condenser is cooled with ice water, and the receiver is immersed in an ice bath. The fraction boiling at 25-55°, wt. 170-190 g., is redistilled through a 60-cm. column packed with glass helices or a column of similar efficiency to give 150-170 g. (63-71%) of 1,4-pentadiene, b.p. 26-27.5°/760 mm., 1.3861-1.3871 (Note 5). 

Microsegregation was studied by electron microprobe analysis of samples cooled at 0,5°C/s and quenched from just below the solidus temperature. Line scans were performed in selected areas of the specimens. Before analysis the samples were etched and the lines to be traversed were marked with microhardness indentations. Strongly etched specimens were repolished before measuring. Two lines were selected from different areas in each specimen, on the same principle as that for selecting lines for dendrite arm measurement. Consequently, in most cases secondary dendrite arms were crossed at right angles but some primary dendrites were intersected also. A typical example of a traverse for analysis is shown in figure 1.9. 

Overheating beyond their thermal limits will soften some monolithic toppings. If so, these toppings may appear to be partly cured, and show maiks and indentations. They will usually re-harden when they are cooled. (See also Item II-... 

The composite, metal substrate, and braze foils (two layers, -100 pm total thickness) were sliced into 2.54 cm x 1.25 cm x 0.25 cm pieces and ultrasonically cleaned in acetone for 15 min. The braze foil was sandwiched between metal and composite, and a normal pressure of 1.2-4.7 kPa (0.38-1.5 N) was applied to the assembly. The assembly was heated in a furnace to -15-20 °C above the braze liquidus under vacuum (10 torr), soaked for 5 min., and slowly cooled to room temperature. The brazed joints were prepared for metallography and examined with a Scanning Electron Microscope (SEM) coupled with energy dispersive x-ray spectroscope (EDS) on a JEOL-840 A unit. Microhardness scans were made with a Knoop micro-indenter on a Struers Duramin A-300 machine under a load of 200 g and loading time of 10 s. 

In these condensers the cooling surface is enlarged by the provision of indentations, undulations, bulbs or a screw structure. 

West s condenser provided with indentations, narrow jacket and cooled ground joint (socket)... 

---