Abstract
The paper is devoted to the research of the effect of ultrasonic postprocessing—specifically, the effects of ultrasonic cavitation-abrasive finishing, ultrasonic plastic deformation, and vibration tumbling on surface quality, wear resistance, and the ability of real aircraft parts with complex geometries and with sizes less than and more than 100 mm to work in exploitation conditions. The parts were produced by laser powder bed fusion from two types of anticorrosion steels of austenitic and martensitic grades—20Kh13 (DIN 1.4021, X20Cr13, AISI 420) and 12Kh18N9T (DIN 1.4541, X10CrNiTi18-10, AISI 321). The finishing technologies based on mechanical action—plastic deformation, abrasive wear, and complex mechanolysis showed an effect on reducing the submicron surface roughness, removing the trapped powder granules from the manufactured functional surfaces and their wear resistance. The tests were completed by proving resistance of the produced parts to exploitation conditions—vibration fatigue and corrosion in salt fog. The roughness arithmetic mean deviation Ra was improved by 50–52% after cavitation-abrasive finishing, by 28–30% after ultrasonic plastic deformation, and by 65–70% after vibratory tumbling. The effect on wear resistance is correlated with the improved roughness. The effect of used techniques on resistance to abrasive wear was explained and grounded.
Highlights
Technologies 2020, 8, 73 methods are oriented on the treatment of linear surfaces as mechanical abrasive [16,17,18], laser–plasma [14,20,21,22,23], ion–plasma, or electron beam [27,28,29] polishing that showed its effectiveness only on small flat areas with achievable microroughness more than 1 μm, ultrasonic plastic deformation, or their combination
Due to high cooling rates obtained during laser powder bed fusion, the produced samples have a fine structure that corresponds and is equal to the processes obtained in cast samples by quenching in liquid [71,72,73,74,75] that are not available for other types of additive manufacturing based on particles’ adhesion and diffusion [47,48]
The results of the study showed that the provided mechanical methods of finishing have a positive effect on submicron roughness; they allow reduction of the average roughness parameter by 1.5–3.5 times (Figures 5, 6 and 7c,d) and removal of the trapped powder granules from the additively produced surfaces (Figure 7a,b), which should allow a significant improvement of the functionality of the surfaces in the friction pairs and tight contact with detachable fasteners of parts
Summary
(anisotropy of properties, natural profile waviness, surface roughness parameter Ra higher than 6.3 μm, trapped unmelted granules, side effect) despite the evident advantages [9,10], especially concerning the production of the functional wear-resistant responsible products for more complex mechanisms for the needs of the transport, aircraft, and aerospace industries [11,12]. Another problem is the postprocessing of the obtained surfaces with a complex character and internal cavities that are mostly required for the parts produced by additive manufacturing [13,14,15]. Surface roughness parameters of additively manufactured parts are critical for the nuclear industry to provide smooth contact between rods and volumetric mesh structures [45,46] to ensure smooth surfaces of nozzles and dies [47,48]
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