J Am Ceram Soc. 2019;102:5691–5698. wileyonlinelibrary.com/journal/jace | 5691 © 2019 The American Ceramic Society
1
|
INTRODUCTION
Liquid phase sintering (LPS) is used as a mechanism for im-
proving the mechanical properties of sintered steels, since it
accelerates diffusion and homogenization of the alloying ele-
ments across the microstructure. The successful performance
of LPS relies on the distribution of the alloying elements
within the microstructure, close dimensional tolerances, and
the densification of the steel. Therefore, it is strongly related
to the features of the liquid phase: the wettability of the pro-
moted liquid over the Fe particles, the infiltration capacity of
the liquid through the porosity network and the liquid‐solid
interaction. Considering a transient liquid phase, if the liquid
wets the solid (θ < 90°), the liquid phase tends to spread over
the powder particles surface, thus favoring the capillarity
action among particles immersed in the liquid and enhanc-
ing the material densification.
1
The liquid‐solid interaction
(inert, reactive or dissolutive
2‒6
) across the interface highly
influences the wetting and the infiltration during the sinter-
ing cycle. Creating a favorable wetting case is not exclusively
linked to the liquid‐solid interaction, but it is also related to
the solid surface conditions. The oxide layer naturally cover-
ing any metallic surface must be removed prior to the melting
of the promoted liquid, so that it can wet and spread over the
solid surface. Hence, the favorable wetting scenario with no
presence of unreduced oxides depends on different factors,
being necessary to define a wetting system,
7,8
composed of
the environmental conditions (temperature, atmosphere and
pressure), the solubility between phases, the chemical com-
position of the present phases and the surface characteristics.
The careful control of the whole liquid‐solid–atmosphere be-
havior is the key for a successful wetting performance, since
it determines the change from an unfavorable wetting situa-
tion toward positive wetting conditions.
The aim of the current study was to analyze the feasibility
of a newly designed B‐free alloy for multiple applications:
as a liquid phase promoter for sintered steels and as a filler
material for joining PM steels through the sinter‐brazing
technique. The last one consists a joining method of metal-
lic components in which sintering and brazing of the desired
parts take place simultaneously, which gives the opportu-
nity of manufacturing intricate shapes of dissimilar materi-
als, while reducing the steps of the manufacturing route and
further machining operations.
9
There is a tight connection
between the wetting behavior of the liquid and its brazeabil-
ity,
10‒12
since the molten alloy must wet the solid and spread
Received: 9 March 2018
|
Accepted: 2 April 2019
DOI: 10.1111/jace.16518
SPECIAL ISSUE ARTICLE
Novel multiuse liquid phase promoter for PM components
Andrea Galán‐Salazar
|
Mónica Campos
|
José Manuel Torralba
Materials Sci. and Eng. Dept., Universidad
Carlos III de Madrid, Leganés, Madrid,
Spain
Correspondence
Andrea Galán‐Salazar, Materials Sci. and
Eng. Dept., Universidad Carlos III de
Madrid, Leganés, 28911 Madrid, Spain.
Email: andrea.galan@uc3m.es
Funding information
DIMMAT, Grant/Award Number: S2013/
MIT‐2775
Editor: Eugene Olevsky
Abstract
The aim of this work was to characterize the behavior of a novel multiuse B‐free
alloy that was designed as a liquid phase promoter and as a filler material for sinter-
ing and brazing steels in N
2
‐H
2
. Through thermodynamic calculations, a new Cu‐Fe‐
Ni‐Si alloy (named LP) has been designed showing a proper melting point suitable
for being used at temperatures below 1100°C, with good wetting behavior that allows
it use as brazing material and liquid phase former. This new boron‐free alloy has
shown good dimensional behavior, good brazeability, and competitive mechanical
properties. These demonstrated features allow the developed alloy it use as braze ma-
terial for PM parts in industrial furnaces as well as master alloy to promote transient
liquid phase in PM structural steels.
KEYWORDS
dilatation/dilatometry, iron/iron compounds, joints/joining, sinter/sintering, wetting