Solidificação rápida e conformação por spray de ligas ferrosas amorfizáveis a partir de ferros fundidos com adição de boro e nióbio
Abstract
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.