INFLUENTIAL FACTORS ON THE TOUGHNESS OF NANOSTRUCTURED HARD METALS

1
INFLUENTIAL FACTORS ON THE TOUGHNESS OF
NANOSTRUCTURED HARD METALS

• Tamara Aleksandrov Fabijanic1, Ivan Jeren2, Vesna
  Puklavec2
• 1Faculty of Mechanical Engineering and Naval
  Architecture, Ivana Lucica 5, Zagreb
• 2Alfa Tim d.o.o., Culinecka cesta 25, Zagreb
• Corresponding author tamara.aleksandrov_at_fsb.hr

ABSTRACT The procedure of toughness
determination on nanostructured hard metals is
described in the paper. Toughness is determined
with the use of Palmquist toughness test by
measuring the total length of cracks emanating
from the four corners of a Vickers hardness
indentation using the load of 294 N according to
ISO 280792009. The specimens of nanostructured
hard metals were developed in the company Alfa
tim d.o.o. by conventional powder metallurgy
process varying the parameters related to
technological process of obtaining such as the
sintering temperature and input variables such as
percentage of Co and grain growth inhibitors. The
measurements on developed specimens were carried
out in the Laboratory for Testing Mechanical
Properties of Materials at the Faculty of
Mechanical Engineering and Naval Architecture.
The results of the carried measurements and
influence of certain factors were analysed.
Certain conclusions about influential factors on
the achieved toughness of nanostructured hard
metals have been brought. Keywords fracture
toughness, Palmquist test, nanostructured hard
metals
PALMQIUST TEST
The toughness value can be calculated using two
methods Method 1 - Ratio of indent load to
crack length , WG
where WG Palmquist toughness P
indentation force, N T total crack length, mm
Method 2 - Calculated value of toughness, WK
where WK - Palmquist fracture toughness A - is
an empirical constant with a value of 0.0028, H
- is the hardness in N/mm at a load of 30 kgf
Figure Vickers indentation with characteristic
values
a)

b) Figure Microstructure of
developed nanostructured hard metals on SEM a)
Microstructure of the sample 366-1, sintering
temperature 1400C, 10 000 X b) Microstructure
of the sample 376-1, sintering temperature
1420C, 10 000 X
EXPERIMENTAL PROCEDURE
ANALYSIS OF THE RESULTS
a)

b) Figure a)
Palmquist fracture toughness versus Vickers
hardness of the batch DN 2-5 CRV-9/366
b) Palmquist fracture toughness versus Vickers
hardness of the batch DN 2-5 V-9/369
a)

b) Figure Starting powders analyzed on FESEM a)
WC D-N 2-5 with addition of VC b) WC D-N 2-5 with
addition of VC i Cr3C2
Table Batches characteristics
Batch Starting powder Grain grow inhibitors Grain size, nm Co content,
DN 2-5 CRV-9/366 WC-DN-2-5 VC, Cr2C3 150 9
DN 2-5 V-9/369 WC-DN-2-5 VC 150 9
DN 2-5 CRV-6/376 WC-DN-2-5 VC, Cr2C3 150 6
DN 2-5 CRV-4/379 WC-DN-2-5 VC, Cr2C3 150 4
a)

b) Figure a)
Palmquist fracture toughness versus Vickers
hardness of the batch DN 2-5 CRV-6/376
b) Palmquist fracture toughness versus Vickers
hardness of the batch DN 2-5 CRV-4/379
Figure Samples developed by conventional powder
metallurgy process
CONCLUSION On the basis of conducted research
can be concluded that Palmquist toughness values
do not change with the change of Vickers hardness
obtained by sintering on different temperatures.
In another words sintering temperature doesnt t
influence on the achieved values of Palmquist
fracture toughness of nanostructured hard metals.
Therefore can be confirmed that the Palmqiust
fracture toughness does not decrease with
increasing hardness values what is a case in
conventional hard metals as mentioned in already
published literature. Measured values of
Palmquist fracture toughness for the samples from
the batches DN 2-5 CRV-9/366, DN 2-5 CRV-6/376
and DN 2-5 CRV-4/379 vary for approximately 2
what can be attributed as a measuring error.
Continuous small decrease of Palmquist fracture
toughness is noted only for the batch DN 2-5
V-9/369 where grains grow inhibitor is VC and
differ from other bathes where grain grow
inhibitor are VC and Cr3C2. Mentioned decrease is
very small and can be explained as a measuring
error. Still, should not exclude the fact that
grain grow inhibitors influence on the fracture
toughness behaviour of nanostructured hard
metals. Further investigations are needed to be
done to confirm or reject above mentioned fact.
Also, influence of cobalt contents on Palmquist
fracture toughness is noted the measured values
of Palmquist fracture toughness decreases with
decreasing cobalt content.