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Previous issue date: 2015-07-31 === Não recebi financiamento === The amorphizable ferrous alloys and/or nanocrystalline ones have high
hardness properties and wear resistance which are important technologically.
Rapid solidification process with cooling rate between 102 - 106 K/s leads to
high hardness properties and wear resistance. The objective of this work is the
study and the characterization of microstructure and hardness of white cast iron
and nodular gray by rapid solidification, exploring techniques that impose
different cooling rates, with different additions of Boron and addition or not of
Niobium. The alloys were processed by Discovery® Plasma and melt-spinning,
namely: (Fe65Cr17Mo2C14Si2)100-xBx (Fe65Cr17Mo2C14Si2)88B8Nb4 and
(Fe75Nb6C10Si4)100-xBx (at%). The characterization was made by X-ray diffraction
(XRD), differential scanning calorimetry (DSC), optical microscopy (OM),
scanning electron microscopy (SEM), transmission electron microscopy (TEM)
and Vickers microhardness (HV). The (Fe65Cr17Mo2C14Si2)88B8Nb4 (at%) alloy
was selected to spray forming and laser cladding processes obtaining deposit
and overspray powders into different particle size from 20 μm and more than
180 μm. The alloys were copper mold cast resulting in plate samples with
thickness of 1.0 and 2.0 mm. The cast iron plate microhardness, without Boron
and Niobium, showed around 650 HV and about 1400 HV after the addition of
12 at% of Boron. The (Fe65Cr17Mo2C14Si2)88B8Nb4 (at%) alloy has
nanocrystalline microstructure after spray forming in the deposit and overspray
powders and Vickers microhardness value of about 1040 HV in the deposit. For
these alloys it was required high cooling rates of about 106 K/s to obtain
amorphous phase by melt-spinning process. The laser cladding process used
overspray powders to produce coatings with microhardness up to around 1300
HV. It was possible using power 200 W, in slower scanning travel speeds (6.7
or 10.0 mm/s). The laser cladding process presented good perspectives of
application in order to produce wear abrasion and corrosion resistant coatings. === Ligas ferrosas amorfizáveis e/ou nanocristalinas apresentam
propriedades como alta dureza e resistência ao desgaste, o que as torna
interessantes tecnologicamente, A via de processamento por solidificação
rápida, com taxas de resfriamento entre 102 – 106 K/s garante esta alta dureza
e resistência ao desgaste. O objetivo do presente trabalho é o estudo e
caracterização da microestrutura e microdureza do ferro fundido branco e
cinzento nodular através da solidificação rápida, explorando técnicas de
solidificação rápida sob diferentes taxas de resfriamento, diferentes teores de
boro e adição ou não de nióbio. As ligas foram processadas via Discovery®
Plasma e melt-spinning, sendo elas: (Fe65Cr17Mo2C14Si2)100-xBx,
(Fe65Cr17Mo2C14Si2)88B8Nb4 e (Fe75Nb6C10Si4)100-xBx. A caracterização foi feita
por difração de raios-X, calorimetria diferencial de varredura, microscopia ótica,
microscopia eletrônica de varredura e de transmissão, além de microdureza
Vickers. Selecionou-se para a conformação por spray e Laser Cladding a liga
(Fe65Cr17Mo2C14Si2)88B8Nb4, obtendo depósito e pós overspray em diferentes
granulometria, a partir de 20 μm e superior a 180 μm. A fundição em coquilha
de cobre na forma de chapas com espessuras de 1,0 e 2,0 mm apresentaram
aumento na microdureza de aproximadamente 650 HV, sem Boro, para
aproximadamente 1400 HV, com adição de 12%at. boro. A conformação por
spray da liga (Fe65Cr17Mo2C14Si2)88B8Nb4 (%at.) apresentou microestrutura
nanocristalina no depósito e no pó overspray e valor de microdureza Vickers de
aproximadamente 1040 HV no depósito por spray. Para as ligas estudadas
foram necessárias altas taxas de resfriamento, impostas por melt-spinning,
aproximadamente 106 K/s, para obtenção de fase amorfa. O processamento
através de laser cladding a partir do pó overspray levou à microdureza Vickers
de 1300 HV, aproximadamente, com potência Laser de 200 W utilizando
menores velocidades de varredura, notadamente 6,7 ou 10,0 mm/s, mostrando
boas perspectivas de aplicações como recobrimentos resistentes ao desgaste
e corrosão através laser cladding.
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