The company projects worldwide tablet sales worldwide to touch 229 million units this year, which is a 11 percent growth over 2013 and represents 9.5 percent of total worldwide device sales in 2014. In 2013, tablet sales grew 55 percent.
In tablets, the downward trend stems from the slowdown in basic ultramobiles, new sales of iPads and Android tablets, and the lifetime extension of current tablets to three years by 2018, Gartner said in a statement.
It projects over 90 million fewer new tablet purchasers and 155 million fewer tablet replacements through 2018, it added.
"Some tablet users are not replacing a tablet with a tablet, they are favouring hybrid or two-in-one devices, increasing its share of the ultramobile premium market to 22 percent in 2014, and 32 percent by 2018," Gartner Research Director Ranjit Atwal said.
Global shipments of devices -- PCs, tablets, ultramobiles and mobile phones -- for 2014 are estimated to reach 2.4 billion units in 2014, a 3.2 percent increase from 2013.
"The device market continues to evolve, with the relationship between traditional PCs, different form factor ultramobiles (clamshells, hybrids and tablets) and mobile phones becoming increasingly complex," Atwal said.      

Mobile phone segment will continue to grow in 2014 due to strong sales of lower-end smartphones. Sales of basic smartphones (including midrange Android devices) are projected to grow 52 percent in 2014, while utility smartphone units (including low-end Chinese white box devices) will double.
In 2015, Gartner estimates that shipments of Android devices will reach over one billion in emerging markets, driven by sales of lower-cost products.
Apple's new devices, which target the premium market, will continue to help drive iOS volumes. These devices will benefit from a controlled and integrated ecosystem, a focus on the user experience and a leading enterprise tablet position, the research firm added.