Optimal Sintering Procedure to Fabrication of Functionally Graded

Hydroxyapatite-Titanium

Ali Shahrjerdi1, 2, a, F. Mustapha 3,b , S.M. Sapuan1, c, M. Bayat4, d, D.L.A. Majid 3,e and R.Zahari3,f

1Department of Mechanical and manufacturing Engineering, Universiti Putra Malaysia, 43400,

Selangor, Malaysia

2Department of Mechanical Engineering, University of Malayer, Iran

3Department of Aerospace Engineering, Universiti Putra Malaysia, 43400, Selangor, Malaysia

4Department of Civil Engineering, Aalborg University, 9000 Aalborg, DK

aailshahrjerdi2000@yahoo.com,

bfaizal@eng.upm.edu.my,

csapuan@eng.upm.edu.my,

dmeb@civil.aau.dk

Keywords: Hydroxyapatite-Titanium, FGM, Sintering, Pressure-less method

Abstract. Functionally graded metal-ceramic composite was fabricated by pressure-less sintering.

The pure metallic component (Ti) and the pure ceramic component (HA) were located at the ends of

a cylindrical specimen. Titanium and-Hydroxyapatite were utilized as a metallic and ceramic layer.

The target sample thickness was 6 mm with radius cylindrical 20 mm. The sample was made from

the cylindrical type of carbon die consisting of 5 layers. The composition of layers were

100%Titanium; 75 % Titanium +25% HA; 50% Titanium +50% HA; 25% Titanium+75% HA, and

100% Hydroxyapatite. The optimum thermal load mapping was obtained experimentally. The

properties of all FGM products were characterized by shrinkage, optical-microscope, energy

dispersive spectrometry (EDX) scanning electron microscope (SEM). The grade of the FGM

material was proven by comparing amount of shrinkage after sintering. Result from optical

micrograph, SEM and EDX indicated that the HA-Ti FGM could be produced successfully by using

the optimal sintering procedure that was highlighted in this paper.

Introduction

Functionally graded materials (FGMs) usually are composed of a ceramic and a metal at which

the volume fraction of the two materials is varied. Functionally graded materials (FGMs) are those,

in which the volume fraction of the two or more materials is varied, according to a power-law

distribution as a function of position along certain dimension (s) of the structure [1].

Bio-medical applications are new field to FGMs as an implant and artificial parts of body [2].

Human body is supported by 206 bones and each of them directly or indirectly affects our brain and

other organs. Efforts of researchers are established to find a new material that can work as

replacement for bones. Several different physical and chemical methods depending on type of

materials and facilities are used to fabricate FGMs [3]. A best-fit single method to fabricate of FGM

is difficult to define due to each method has its own advantages and drawbacks. HA and Ti are two

important materials that have been investigated in some studies as FG materials [4; 5] . Due to their

advantages in biomedical, mechanical and biocompatibility properties of FG produced, some studies

have been reported [6]. The effect of Ti additions through the composition, microstructure, thermal

stability and the bonding strength of HA/Ti coating using hydrothermal–electrochemical technique

was investigated by Xiao et al. [7]. Fabrication of HA/Ti as a FG dental implant using CIP and

sintering method was experimented by Watari et al. [8] to ensure both mechanical and

biocompatible properties. Chenglin et al. [4] developed a FG biomaterial in a HA/Ti system by an

optimized powder metallurgical method. They successfully investigated micro-structural analysis

and mechanical tests of the produced FGMs. Chu et al. [5] examined the fabrication of FG

Key Engineering Materials Vols. 471-472 (2011) pp 140-144Online available since 2011/Feb/21 at www.scientific.net© (2011) Trans Tech Publications, Switzerlanddoi:10.4028/www.scientific.net/KEM.471-472.140

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biomaterial HA/Ti by a hot-pressing technique, they [9] also developed and fabricated FG

biomaterial HA/Ti by adopting of the best mixing of their biocompatibility and mechanical

properties. Some porosity reduction and sintering models using pressure-less sintering method was

investigated by Pines and Bruck [10; 11]. The present work focuses on pressure-less sintering

method for fabrication of HA/Ti functionally graded materials. The thermal map is optimized

experimentally and the some physical effects of powders are discussed. Microstructure and

properties of FG samples are evaluated and the gradation of HA/Ti FG cylinder is proven by some

examinations.

Material and Method

HA (SIGMA-ALDRICH, USA) and Ti (SIGMA-ALDRICH, USA) powders are used here as a

ceramic and metallic for the fabrication of FG plate. HA is a biomechanical and cohesive material

having close melting point to Ti. The combination can be an excellent replacement component as a

hard tissue in human body. The maximum difference in the melting points for components in cold

pressing method should be small. It is noted that in order to have a good quality of FG structure, it

needs at least five layers. The best composition (in %weight) of layers have been selected as 100%

pure Titanium; 75% Titanium+25% HA; 50% Titanium+50% HA; 25% Titanium+75% HP; 100%

pure HA. The details of the material can be observed in Figure.1. The powders should be blended

separately for at least 1 hour and together for 5 hours to ensure the maximum dispersion of particles

and can reach to the optimal physical properties. It is noted that the ball milling process the powders

need to dried in an oven at 110oC for approximately 12 hours. This procedure is necessary in order

to have a dry mixture without any moisture. During cold pressing procedure, the green compact is

created using cylindrical type of carbon die with a diameter of 20 mm. It consists of 5 layers with

the same thickness for all of the layers except the top and the bottom layers. In the fabrication

process, the compositions are compacted at 10 (Ton) using uni-axial hydraulic press to make a green

compact. The last step in the fabrication process, green compacts are sintered inside the tube furnace

under flowing mixed argon as to prevent oxidation. The heating map depends on the melting points

of the powders.The heating map is obtained by trial-and-error approach, as to have appropriate

product and optimimal sintering map (see Fig.2). The temperature is increased from 30oC to 1200

oC

during 8 hours. The adhering of each layer to others is directly related to the maximum selected

temperature during sintering. Beside the thermal specification as mention above; another two

parameters, position and direction of the green compact inside the furnace are important. The best

position for the green compact is at the middle of furnace. It is recommended that, the heavier

component should be at the upper surface.

Fig. 1: composition (in %weight) of functionally graded HA/Ti layers

Key Engineering Materials Vols. 471-472 141

Result and Discussion

The gradation of the FG HA-Ti is proven by using shrinkage measurement. Linear shrinkage is

one of the parameter needed evaluating the quality of the gradation of the component in the FG

samples, the process can be calculated by accurately measuring of the green compact and then

comparing with the size of the sample after sintering as shown in Figure 3. It is clear that, the linear

variations of Ti to volumetric HA by scanning electron-microscope (SEM) for thickness and also

for each layer individually (Figs.4). Figure 5 record the chemical component from full Ti and 75%

HA by EDX examination. The percentage of Calcium that indicates the HA is decreased from Fig.

5a gradually in to full percentage of Ti in Fig.5b

Fig.2: Optimal sintering map

Fig.3: Titanium percentage against shrinkage amount

Fig.4: Digital SEM image of HA/Ti

SEM image of layers in experiments (Accelerating Voltage: 15.0 kV Magnification: 1000)

142 Composite Science and Technology

Fig. 5(a) Fig 5(b)

Fig.5(a) and Fig. 5(b): EDX examination for full Ti and 75% HA+25% Ti

Summary

An optimum heat sintering map with Pressure-less powder metallurgy procedure is presented to

fabricate the HA/Ti functionally graded (FG) cylinder. The gradation of components are considered

from metallic (Ti) end to its ceramic (HA) end. Optimum sintering map has been derived

experimentally. To validate the shrinkage study, SEM and EDX examination are employed. The

structure and composition analysis of the FG cylindrical produced with different layers conforms the

functionality of the design. The linear shrinkage obtained is an appropriate witness of validation.

Acknowledgment

The authors would like to thank to Universiti Putra Malaysia for providing the research grant

(FRGS 07-10-07-398SFR 5523398) for this research work.

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Composite Science and Technology 10.4028/www.scientific.net/KEM.471-472 Optimal Sintering Procedure to Fabrication of Functionally Graded Hydroxyapatite-Titanium 10.4028/www.scientific.net/KEM.471-472.140

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