372595882

COATINGS

JPRS-UMS-92-003 16 March 1992

The High-Temperature Oxidation of a Composite Materiał Consisting of 80% TiB₂ and 20% TiC

927D0090F Ordzhonikidze IZYESTIYA YYSSHIKH UCHEBNYKH ZA VEDENIY: TSYETNA YA METALLURGIYA in Russian No 2, Apr 91 (manuscript recei\ed 1 Mar 90) pp 59-63

[Article by V.S. Shestitko, P.V. Polyakov, and A.M. Golovanets, Light Metals Metallurgy Department, Kras-noyarsk Institute of Nonferrous Metals]

U DC 669.713.7

[Abstract] The authors of the study reported herein used the thermogravimetric method to examine the high-temperature oxidation of a composite consisting of 80% TiB₂ and 20% TiC. A preweighed specimen was hung on a nichrome suspension mounted on the bowl of an analytical scalę and lowered into a shaft fumace that was then heated to a specified temperaturę for a specified time somewhere between 5 and 10 hours. The change in the specimen’s mass as a result of high-temperature oxidation was then determined. The measurements were taken on hot-pressed specimens of the study composite with a close-to-theoretical density at five fixed tempera-tures (°C): 700, 800, 900, 1,000, and 1,100. The kinetic curves plotted for the different heating temperatures and times were not identical. In the initial legs of the curves for all of the study temperatures the researchers observed a reduction in specimen mass that was, upon first approximation, proportional to temperaturę. Also note-worthy was the fact that the “bumup peak” was in the rangę from 3 to 15 minutes from the beginning of the experiment at all temperatures except 900°C. In the case of heating to 900°C, the peak was shifted in time to the rangę of 25-30 minutes. In the cases of heating to temperatures of 700 and 800°C a protective film formed quickly after the “bumup peak,” and the change in mass virtually ceased after the first 1-1.5 hours. At temperatures of 1,000 and 1,100°C, the oxidation curve assumed a parabolic form after a linear segment of mass inerease in the interval from 15 to 30 minutes. Microphotographs of specimens heated to each of the different temperatures were compared. Heating at 700°C resulted in an inerease in surface microirregularities and surface scar-ring. The specimens heated to 800°C exhibited smoothing of the surface and formation of vacancies between the individual conglomerates. At 900°C fusion and even morę surface smoothing occurred along with the formation of fine grains with pores between them. At 1,000°C the grains became Consolidated, and the zones of vacancies between them inereased. At 1,100°C the grains on the specimens’ surfaces became larger once again, fused particles became distinctly apparent, and the zonę of the vacancies inereased. Oxidation of the materiał was found to occur inside the pores of the forming protective film. The oxygen content of the different specimens was also compared. At 700°C the oxygen content dropped sharply farther from the surface. At 800°C the oxygen content deep within the specimens inereased. At 900°C the oxygen content decreased (evi-dently the film formed had greater protective proper-ties). The oxygen content at the specimen surface reached a maximum at 1,000°C. Figures 4; references 8 (Russian).

Selected Features of Pulsed Laser Hardening of Titanium Alloys

927D0089M Moscow FIZIKA I KHIMIYA OBRABOTKIMATERIALOY in Russian No 6,

Nov-Dec 91 (manuscript received 26 Oct 90) pp 130-134

[Article by A.P. Lyubchenko, Ye.A. Satanovskiy, V.N. Pustovoyt, G.I. Brover, V.N. Varavka, and Ye.A. Katsnelson, Kharkov and Rostov-na-Donu]

UDC 669.14.018:621.785:535.211

[Abstract] The authors of the study reported herein examined selected characteristic features of the laser surface hardening of titanium alloys. Specimens of VT3-1 titanium alloy were subjected to pulsed laser treatment by a Kvant-16 laser with a power flux density of 100 to 150 kW/cm². The following powders were used during the laser surface alloying: standard carburizer (birch tar oil), ferrochrome, A1₂0₃, T15K6, a-BN, and molecular boron. Coal-tar vamish was used as a binder. A Neo-phot-21 microscope was used for the metallographic studies, a PMT-3 hardness tester was used for the durability tests, and a DRON-.05 diffractometer was used for the x-ray crystallographic studies. The experi-ments conducted demonstrated that laser surface treatment can indeed harden the surface of titanium alloy specimens, with the degree of hardening depending on the alloying coating selected. A1₂0₃, ferrochrome, T15K6, and a-BN proved particularly effective in improving the basie performance characteristics of the titanium alloys treated. The laser surface treatment regimen tested was found to result in the formation of a rather deep (70 to 100 pm) hardened layer with a hardness exceeding that of the starting metal by a factor of 1.1 to 1.6. This effect was attributed to the concentra-tion and morphological inhomogeneity of the solid Solutions, the formation of a a’ martensite phase, and satu-ration of the alloy with nitrogen and carbon from the air and from the coating. Figures 4; references 3: Russian, Western.

Change in the Structure and Properties of Surface Layers of Titanium Upon Laser Surface Alloying

927D0089L Moscow FIZIKA I KHIMIYA OBRABOTKI MATERIALOY in Russian No 6,

Nov-Dec 91 (manuscript received 13 Feb 91) pp 117-123

[Article by A.N. Bekrenev and Ye.A. Morozova, Samara] UDC 621.793.6:621.375.826

[Abstract] The authors of the study reported herein examined the changes in the structure and properties of