Powder Metallurgy Progress, Vol.11 (2011), No 3-4 320

PREPARATION AND PROPERTIES OF Fe/DIALLYLPHTALATE COMPOSITE

R. Bureš, T. Sopčák, M. Fáberová, V. Kovaľ

Abstract Powder mixture of iron powder ASC 100.29 and diallylphtalate resin with glass fibre filler was prepared. Dependence of basic technological properties of powder mixture on the content of resin were investigated. Composites with 10, 20, 30 and 50 vol.% of resin were prepared using cold die pressing at 800 MPa and curing at 190ºC. Mechanical and electrical properties of composites were evaluated. Properties of investigated composite are superposition of bond phase distribution, amount of polymeric bond and porosity. Homogeneous distribution of diallylphtalate polymer reinforced by glass fibre leads to perspective combination of properties e.g. composite with 20 vol.% of resin: porosity <5%, specific resistivity ~0.1 Ω.m, hardness ~200 HV10 and bend strength TRS 35 MPa. Keywords: powder mixture properties, mechanical properties, resistivity

INTRODUCTION Powder metallurgy (PM) is one of the most important technologis used to produce

composite materials. Soft magnetic materials (SMC) prepared from ferromagnetic powder particle with electric insulation surface layer are used in electrotechnics. As insulation and bond material used are organic, inorganic compounds or their combination [1,2]. Advances in the field of chemical synthesis and materials characterisation are motivation to new wave of interest in composites in last years [3,4]. SMC are produced via PM with utilisation of new compaction techniques. The most economical technologies for SMC production are cold die pressing followed by sintering or MIM technology depending on size and shape [5,6]. However, compaction is influenced by morphology, granulometric composition and mechanical properties of compacted powders. Selecting suitable source powders and optimal compaction technology lead to new SMC with excellent 3D magnetic properties, lower eddy current losses and adequate mechanical properties. Idea of combination of pure iron and thermosetting resin for preparation of SMC is not new. This concept has been known for a long time, but technology of structural parts production and properties of resin were not suitable for mass production. New shaping technologies and new polymeric materials help to remove these limitations. Thermosetting resins are polymeric material that irreversibly cure by heat, chemical reaction or irradiation. Known thermosets are epoxies, polyesters, phenol-formaldehyde resins and diallyl-phtalate resins (DAP) [7]. DAP is suitable for production of mechanically hard composite materials [8].

EXPERIMENTAL MATERIAL AND METHODS Powder mixtures were prepared by mixing iron powder ASC 100.29 Höganäs AB

Sweden (ASC) and commercial diallyl-phtalate resin with glass fibre content Isofast Struers

Radovan Bureš, Tibor Sopčák, Mária Fáberová, Vladimír Kovaľ, Institute of Materials Research, Slovak Academy of Sciences, Košice, Slovak Republic

Powder Metallurgy Progress, Vol.11 (2011), No 3-4 321 Denmark (ISF). DAP Isofast was supplied as granulate, which was milled in a knife mill 3 times at 30 sec. to form a powder. Basic physical properties of powder mixtures were measured by international standards: Apparent Density - MPIF Standard 04, ISO 3923/1, ASTM B 212; Tap Density - MPIF Standard 46, ISO 3953, ASTM B 527; Theoretical Density - MPIF Standard 45, ISO 3927, ASTM B 331; Flow Rate - MPIF Standard 03, ISO 4490, ASTM B 213; Flow Rate - Plastics, determination of flowability STN EN ISO 6186; Plastics, determination of apparent density of material that can flow through a specified funnel ČSN EN ISO 60.

Fe-ISF powder mixtures with 10, 20, 30 and 50 vol.% of Isofast were homogenised in mechanical mixer Turbula. Samples in the shape of cylinders with diameter 10 mm and prism 4x5x20 mm were prepared by cold die compaction at 800 MPa pressure. Green compacts were cured at 190ºC in electric furnace in air. Metallographic sample were prepared for investigating microstructure and porosity of composites. Metallographic light inverted microscope Olympus GX71 equipped with the possibility to observe in polarised light was used. Metallographic images were analysed using software ImageJ. Mechanical properties were evaluated by measurement of Vickers hardness (HV10) STN EN ISO 6507-1 and transverse rupture strength (TRS) ISO 3325.

Electrical properties were analysed using impedance analyzer Agilent model 4294A. A two-point configuration was used for the AC resistivity measurement. All experiments were performed at room temperature in air.

RESULTS AND DISCUSSION

Physical properties of mixtures Physical properties of Fe-ISF mixtures were measured using standards for metallic

and polymeric powder materials. Relative apparent density, which is relative to absolute density of mixture, increased with increasing amount of Isofast in powder mixture. Table 1 shows the increase of relative tap density with increasing amount of Isofast indicating better densification of mixtures with higher content of Isofast for conditions of cold die compaction, mainly in first stage of reinforcement of powder particles.

Tab.1. Physical properties of powder mixtures Fe-ISF at temperature 21°C, relative humidity 48 - 50 %.

Powder mixtures [vol.%]

Apparent density ρa[g/cm3]

Tap Density

ρτ [g/cm3]

Hausner ratio

Theoretical density ρth

[g/cm3]

Relative Apparent Density

[%]

Relative Tap

Density [%]

Measured by funnel diameter d = 4 mm

ASC5ISF 2.97 3.85 1.296 7.523 39.48 51.18 ASC 10ISF 2.94 3.83 1.303 7.201 40.83 53.19 ASC15ISF 2.88 3.71 1.288 6.879 41.87 53.93 ASC20ISF 2.86 3.66 1.280 6.558 43.61 55.81 ASC25ISF 2.84 3.62 1.275 6.236 45.54 58.05 ASC30ISF 2.67 3.53 1.322 5.914 45.15 59.69 ASC40ISF 2.52 3.32 1.317 5.270 47.82 63.00

Powder Metallurgy Progress, Vol.11 (2011), No 3-4 322

Powder mixtures [vol.%]

Apparent density ρa[g/cm3]

Tap Density

ρτ [g/cm3]

Hausner ratio

Theoretical density ρth

[g/cm3]

Relative Apparent Density

[%]

Relative Tap

Density [%]

Measured by funnel diameter d = 15 mm

ASC50ISF 2.38 3.03 1.273 4.627 51.44 65.49 ASC60ISF 2.15 2.73 1.270 3.983 53.98 68.54 ASC70ISF 1.87 2.38 1.273 3.339 56.00 71.28 ASC80ISF 1.44 2.02 1.403 2.695 53.43 74.95 ASC90ISF 1.10 1.54 1.400 2.052 53.61 75.05

ISF (milled) 0.79 1.12 1.418 1.408 56.11 79.55

Tab.2. Flow rate of Fe-ISF mixtures measured by funnel of different diameters d.

Powder mixtures [vol.%]

Flow rate d = 2.5 mm

Flow rate d = 4.0 mm

ASC5ISF 30.0s (30.0s/50g = 0.600) uniform flow

7.2s (7.2s/50g = 0.144) uniform flow

ASC 10ISF 33.4s (33.4s/50g = 0.668) uniform flow

7.6s (7.6s/50g = 0.152) uniform flow

ASC15ISF 35.4s (35.4s/50g = 0.708) uniform flow

7.8s (7.8s/50g = 0.156) uniform flow

ASC20ISF 38.3s (38.3s/50g = 0.766) discontinuing

flow

8.3s (8.3s/50g = 0.166) uniform flow

ASC25ISF non free flowing

9.7s (9.7s/50g = 0.194) uniform flow

ASC30ISF non free flowing

10.5s (10.5s/50g = 0.210) uniform flow

ASC40ISF non free flowing

12.95s (12.95s/50g = 0.259) discontinuing

flow

d = 10 mm d = 15 mm d = 25 mm

ASC50ISF 7.9s (7.9s/150g = 0.053) discontinuing flow

3.3s (3.3s/150g = 0.022 ) uniform flow

0.8s (0,8s/150g = 0.005) uniform flow

ASC60ISF 10.9s (10.9s/150g = 0.073) discontinuing

flow

3.7s (3.7s/150g = 0.025) uniform flow

1.6s (1.6s/150g = 0.011) uniform flow

ASC70ISF non free flowing

non free flowing 2.6s (2.6s/150g = 0.017) uniform flow

ASC80ISF non free flowing

non free flowing 4.0s (4.0s/150g = 0.027) discontinuing

flow ASC90ISF non free flowing

non free flowing non free flowing

ISF (milled) non free flowing non free flowing non free flowing

Powder Metallurgy Progress, Vol.11 (2011), No 3-4 323

Flowability of mixtures is documented in Table 2. Flowability is a basic technological parameter, influenced by velocity and mode of die filling during compaction. Values of flow rate strongly depend on mixture composition. Mixtures with more than 90 vol.% of Isofast are non free flowing due to low specific density. Values of flow rate and uniform flow of mixtures under 30 vol.% of Isofast prove good performance of die filling, which is confirmed by values of Hausner ratio in Tab.1.

Metallography Observation of one place of the sample in normal and polarised light allowed us to

evaluate pore and polymer distribution, as it shown in Fig.1. In normal view, it is not possible to recognize Isofast and pores. Isofast is visualised as light green phase while pores are black in polarised light. Area fractions of pores were measured using digital image analysis.

Fe10ISF, LM Fe10ISF, LM

polarized light Fe20ISF, LM Fe20ISF, LM

polarized light

Fe30ISF, LM Fe30ISF, LM

polarized light Fe50ISF, LM Fe50ISF, LM

polarized light Fig.1. Microstructure of Fe-ISF composites, LOM normal and polarized light.

Pores area fraction increase with increasing amount of ISF addition as is documented in Table 3. Measured value of area fraction of ISF is systematically lower than nominal addition of ISF, as it is presented by Lecuona [9]. Differences between value of volume and area fraction increase, as much as measured shape differs from spherical shape. The results of measurement of area fraction of ISF are undervalued more than values of area fraction of pores, due to shape differences.

Tab.3. Area fraction (AF) of pores and resin measured in random plane on metallographic cut.

sample AF of pores [%] Std. deviation AF of resin [%] Std. deviation Fe10ISF 1.76 0.61 4.66 0.29 Fe20ISF 4.58 1.29 12.15 2.73 Fe30ISF 12.06 1.59 28.96 1.86 Fe50ISF 22.62 2.33 45.92 1.86

Powder Metallurgy Progress, Vol.11 (2011), No 3-4 324

Distribution of the polymeric phase is relatively homogeneous in volume of the sample. Primary iron particles are connected through polymeric bonds only. The mechanical and electrical properties of investigated composites are dependent on form of distribution of polymeric bond phase in the volume of material.

Mechanical properties In Table 4 are documented hardness and bend strength of prepared composites.

Tab.4. Selected mechanical properties ASC-ISF composites.

Sample HV10 TRS [MPa] Fe10ISF 178 39.87 Fe20ISF 198 35.15 Fe30ISF 178 39.87 Fe50ISF 211 32.47

Mechanical properties of Fe-ISF composites are strongly dependent on Isofast

content, but the dependence of hardness and bend strength on amount of Isofast is not simple increase for all ranges of material compositions. Pure Isofast after curing is thermosetting polymer with 270 of hardness HV10 and ~100 MPa of bend strength TRS. Resulting mechanical properties are superposition of amount of Isofast and porosity of the composites.

Electrical properties Figure 2 shows the plot of the electrical resistivity of the composites as a function

of mass fraction of the ISOFAST. The electrical measurements for the specific electrical resistance assessment were carried out at room temperature with a measuring signal of 500 mV and frequency of 10 kHz.

Fig.2. The electrical resistivity as a function of Isofast content.

As expected, the resistance of samples against the electrical current increases with increasing amount of dielectric material added into Fe based micro-composites. An increase in the specific electrical resistivity is nearly linear for the compositions with an addition

Powder Metallurgy Progress, Vol.11 (2011), No 3-4 325 of ISOFAST higher than 20 vol.%. The samples with 50 vol.% of ISOFAST exhibited resistivity values greater than 0.7 Ω.m.

CONCLUSIONS Basic technological properties of powder mixtures Fe-Isofast were measured for

different conditions according the standards used for metallic and polymeric powders. It was found that mixtures under 30 vol.% of Isofast can be treated as metallic powder.

Composites Fe-ISF with 10, 20, 30 and 50 vol.% of Isofast were prepared using cold die compaction at 800 MPa of pressure and curing at 190ºC in air.

Homogeneous distribution of diallylphtalate polymer, reinforced by glass fibre, leads to perspective combination of properties. Fe20ISF composite with porosity <5% is material with specific resistivity ~0.1 Ω.m, while hardness is ~200 HV10 and bend strength TRS is 35 MPa. Investigated composite prepared via conventional PM technology is potentially applicable in electrotechnics where dielectric strength and high hardness under high humidity and temperature must be maintained.

Acknowledgement Presented results were obtained within the work on the projects VEGA 2/0149/09

and VEGA 2/0053/11.

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