研究目的
A study of features of the structural state, phase transformation and properties of titanium surface layers during LSA of a single layer chromium coating, and also establishment of rational production regimes this treatment.
研究成果
For the minimum laser beam movement rate in question (0.5 mm/sec) during LSA of titanium with chromium there is typically formation of a surface layer with a low microhardness in the central region of the melt. An increase in rate to 1.66 mm/sec leads to preparation of uniform high values of microhardness, i.e., 9000 – 9200 MPa. However, presence of microcracks arising during rapid cooling of surface layers gives rise to high brittleness. An increase in laser beam movement rate to 2.0 mm/sec (beam operating time 1.25 sec with power density of 128.4 W/mm2 ) forms a structure with a retained high microhardness and reduced brittleness, which is connected with implementation of martensitic α → β6-transformation.
研究不足
The permissible upper limit for rate should provide complete melting of the original coating and formation of a molten bath with a depth of not less than 15 – 20 μm. The acceptable lower limit for rate should exclude excess metal evaporation of an original coating and provide preparation of a quite alloyed surface layer with improved structure and properties.
1：Experimental Design and Method Selection:
Laser surface alloying (LSA) was conducted in a Katyn’ continuously operating unit. Titanium surface microhardness was 1800 MPa, and the thickness of the original chromium plated coating for a titanium surface was 10 μm. Laser radiation power P = 630 W. The diameter of the local laser beam spot was
2：5 mm that provided a radiation power density of 4 W/mThe laser beam movement rate over the surface vl = 5, 66, and 0 mm/sec. Sample Selection and Data Sources:
The object studied was commercially pure titanium alloy VT1-0 containing, wt.%:
3：3 Fe, 1 Si, 07 C, 04 N, 01 H, and 2 O. List of Experimental Equipment and Materials:
Katyn’ continuously operating unit, CO2-Laser.
4：Experimental Procedures and Operational Workflow:
Formation of a molten region with a power of 220 W was not observed since chromium, as also iron, are classified as elements having a high melting temperature and high radiation reflection coefficient.
5：Data Analysis Methods:
The approximate alloying element content in the alloyed zone region was determined by the ratio of the intensity of x-ray radiation for each chemical element with the bath cross sectional area located perpendicular to the direction of laser beam movement. X-ray radiation intensity was measured by the number of pulses recorded by a detector for a certain time.
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