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1

Cavitation erosion phenomenological model of MCrAlY and NiCrMoNbTa metallic coatings deposited via the HVOF method

Szala Mirosław

Tribologia

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2021

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nr 4

45--55

EN

The work describes the phenomenological model of cavitation erosion (CE) elaborated for MCrAlY (where M = Co, Ni or Co/Ni) and NiCrMoNbTa. Coatings were deposited via the HVOF method from CoNiCrAlY, NiCoCrAlY and NiCrMoNbTa feedstock powders. CE tests, conducted according to ASTM G32 standard, indicate that MCrAlYs have a 50% higher maximum erosion rate and twice lower CE resistance than the NiCrMoNbTa coating. CE kinetics of coatings were comparatively studied, combining the mass loss, erosion rate, roughness changes of the eroded surface with microstructure, and mechanical properties of the coatings. Results of SEM analysis of damaged coatings allow identifying the mechanism of CE. In the case of both types of coatings, the erosive damage is initiated at the removal of loose splats, cracking at the border splats and peeling off the coating material, and surface pitting. However, NiCrMoNbTa, due to higher ductility and microstructure homogeneity, presents lesser surface pitting contrary to the MCrAlYs, which have multiphase microstructure higher hardness and consequently was prone to cracking, resulting in the formation of craters and higher surface roughening. The CE mechanism of MCrAlYs was dominated by the brittle mode, while the NiCrMoNbTa coating has mainly a ductile damage behaviour.

PL

W pracy opisano fenomenologiczny model erozji kawitacyjnej (EK) opracowany dla powłok MCrAlY (gdzie M = Co, Ni lub Co/Ni) i NiCrMoNbTa. Powłoki wytworzono metodą HVOF z komercyjnych proszków CoNiCrAlY, NiCoCrAlY i NiCrMoNbTa. Testy erozji kawitacyjnej, przeprowadzone zgodnie z normą ASTM G32, wskazują, że MCrAlY mają o 50% wyższą prędkość erozji i dwukrotnie niższą odporność EK niż powłoka NiCrMoNbTa. Kinetyka erozji kawitacyjnej powłok została poddana analizie porównawczej syntetyzującej utratę masy, szybkość erozji, zmiany chropowatości erodowanej powierzchni z mikrostrukturą oraz właściwościami mechanicznymi badanych powłok. Wyniki analizy SEM uszkodzonych powłok umożliwiły zidentyfikowanie mechanizmu EK. Uszkodzenie erozyjne powłok inicjowane jest w wyniku usuwaniu słabo umocowany cząstek materiału, pękaniu na granicach lameli następnie usuwaniu materiału i tworzeniu wżerów. Jednak NiCrMoNbTa ze względu na wyższą ciągliwość i jednorodność mikrostruktury wykazuje mniejsze wżery powierzchniowe w przeciwieństwie do MCrAlYs, które cechują się wielofazową mikrostruktura o wyższej twardości i w konsekwencji są podatne na pękanie, co powoduje powstawanie dużych wżerów i wyższe chropowacenie powierzchni. Mechanizm erozji kawitacyjnej powłok MCrAlY jest zdominowana przez kruche pękanie, natomiast w przypadku powłoki NiCrMoNbTa dominuje plastyczne odkształcenie.

2

Estimation of Apollo Lunar Dust Transport using Optical Extinction Measurements

Lane J. E., Metzgert P. T.

Acta Geophysica

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2015

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Vol. 63, no. 2

568--599

EN

A technique to estimate mass erosion rate of surface soil during landing of the Apollo Lunar Module (LM) and total mass ejected due to the rocket plume interaction is proposed and tested. The erosion rate is proportional to the product of the second moment of the lofted particle size distribution N(D), and third moment of the normalized soil size distribution S(D), divided by the integral of S(D)⋅D2/v(D), where D is particle diameter and v(D) is the vertical component of particle velocity. The second moment of N(D) is estimated by optical extinction analysis of the Apollo cockpit video. Because of the similarity between mass erosion rate of soil as measured by optical extinction and rainfall rate as measured by radar reflectivity, traditional NWS radar/rainfall correlation methodology can be applied to the lunar soil case where various S(D) models are assumed corresponding to specific lunar sites.

3

Experimental investigation of effects of external loads on erosive wear

Imrek H., Bagci M., Khalfan O. M.

Journal of Achievements in Materials and Manufacturing Engineering

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2009

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Vol. 32, nr 1

18-22

EN

Purpose: The purpose of the paper is to investigate effects of external loads on erosive wear. Design/methodology/approach: In this experimental study, specimens were placed on specially designed a specimen holder and then, external tensile loads corresponding to 0%, 20%, 40% and 60% of the specimen’s yield strength were applied on the specimens. For every load step, the specimens were subjected to 15ş, 30ş, 45ş, 60ş, 75ş and 90ş of erodent impact angles. At the end of the tests, effects of external loads and impingement angles on erosive wear were studied. In the experimental set, dry and compressed air was used to impinge erodents onto the test specimens and subsequent wear was investigated. During the tests, the impingement angles were adjusted by turning the specimen holder around its axis. Erodent particles used were SAE G40 having internal uniform martensitic structure and angular geometry. Determination of erodents speed was achieved with the help of the Rotating Double Disc Method. The speed used in the tests was 30 m/s. Findings: At the end of the tests, erosive wear rates were obtained as functions of stresses and impingement angles. Graphs showing variations of erosive wear rates for load values obtained against every impingement angle and yield stress were drawn. Critical impingement angle and load values at which maximum erosion rate was obtained were determined. Research limitations/implications: In researches made on erosive wears so far; there are only few studies dealing with the effects of external loads on the specimens subjected to erosive wear. By considering that stresses may affect the erosive wear, the stress state around contact area as well as material properties, this experimental study has thus, investigated likely effects of stresses on the erosive wear. With the help of the designed special specimen holder, the specimens were subjected to tensile stresses that are lower than the yield strength of the material and then the erosive wear was investigated. Originality/value: The investigations of effects of external loads on erosive wear.